DAN DUNN SECRET OPERATIVE 48
and The CRIME MASTER

CHAPTER ONE
A Baffling Crime

BECAUSE of the storm that raged outside, the hotel dining room seemed especially cheerful. But Dan Dunn, Secret Operative 48, smiled regretfully across the softly lighted table at his small companion.

"It's too bad, Babs," he remarked. "This rain will keep us in tonight. And we're only going to be here a couple of days! Wouldn't you like to see the town before we leave?"

The youngster looked up from her dessert.

"Oh, Mr. Dan, I'd like awfully to see the town with you," she said. "Maybe it won't rain so hard tomorrow, and then, if nothing happens, we can do it—"

But something was happening, quite unknown to them.

A series of weird and frightful events was beginning, which would change the plans of Secret Operative Dan Dunn and his friend for many days to come, and involve them in adventures of which they could not then dream.

At that moment a forbidding figure was crouched on the hotel fire-escape before a lighted window; and within the room a gray-haired man had risen fearfully from his chair to confront the menace of the night-prowler's pistol.

With a swift movement, the intruder raised the window-sash and grimly, without a word but threatening murder in every silent motion, stepped into the room. Seen in the brighter light, he was a terrifying creature in gloomy, black, rain-sodden garments, .with dirty white hair poking from under his shapeless hat. His face was queerly twisted.

The gray-haired man in the smoking-jacket advanced a step.

"Now, now!" he stammered. "Put that gun away, and let's talk sensibly—"

But the grim apparition only chuckled.

"A-ah! There is no time to talk. You think I'm crazy; but you have only seconds left to think! Your end has come! SO! The pistol speaks... My revenge!... Ah! Now it is done. My voice fades in your ears. The clutch of death—"

Only a soft, spitting sound had come from the queerly shaped pistol muzzle, but the silenced explosion had driven the bullet true to its victim's heart. The gray-haired man staggered backward—then crumpled and lay outstretched on the deep carpet.

"Ah-ha-ha! Revenge is sweet!"

Chuckling, the murderer turned away, to lock the window. Then he glided to the door and tried the key.

Under a shaded studio lamp, the body of the slain man lay quiet. Only faint sounds entered the room—street noises drowned by the gale and deadened by the draperies that covered the one window. The silent minutes stalked by... At last footsteps sounded in the hall.

Meantime, Dan Dunn and little Babs, having finished a leisurely dinner, and discussed the next day's proposed outing, were strolling without haste or apprehension along the corridor toward their rooms.

"We'll get a good night's rest now, Babs, and be up early in the morning. If we're going to see all there is to see in Dallas, one day is none too much, and you'll have to step lively."

"Perhaps I'll make you step lively, Mr. Dan!" laughed Babs. "But just now I do feel more like sleep than anything. It would take something pretty exciting to keep me awake tonight!"

"Wait a minute, Babs!" Dan Dunn had paused in his stride and put out a hand to halt the little girl beside him. "Look! There's a hotel maid rapping on the door next to ours, and there's a funny expression on her face. I think something's the matter... Anyhow, I'll ask her. If there is, we might be able to help."

"Gee!" Bab whispered. "I wonder what COULD be wrong, Mr. Dan?"

The Secret Service Operative stepped forward and touched the maid on the arm, just as she raised it to rap again.

"You can't rouse anybody?" he asked. "Is there any way I can help?"

"Oh, yes, Mister!" she answered. "If you could get up on a chair and look through the transom—I'm afraid Judge Borland's sick. I can't make him hear! And I've been knocking for ten minutes."

"Here's a chair, Mr. Dan!" spoke up Babs. "I'll hold it for you—"

But Dan had already stepped up on the wooden seat and was peering sharply through the transom glass. All at once he whirled about, frowning.

"Get the manager, quick!" he snapped. "Judge Borland's lying on the floor... I can just see his feet, stretched out there."

The maid paled—and turned and ran, without a word, down the hall.

Three minutes later, a very much worried manager appeared, panting from his climb up the stairs.

"What's the trouble?" he gasped. "Is—is this the room? Why! It's Judge Borland's apartment!"

"Yes!" Dan barked. "There's someone lying on the floor—and the door's locked. Key's in the lock inside. We'll have to break in. Smash your door or your window. Which? There's no time to waste! He may be ill, or dying, and even seconds may count!"

The manager thrust out his hands.

"B-Break down the door?" he gurgled in despair. "But can't you get in by the fire-escape?"

"No!" Dan replied. "I tried that while the maid was downstairs looking for you. The one window leading in from the fire escape is locked from the inside, too. So make your choice—but hurry!"

"Th-then we'll have to break down the door, I fear!" the manager quavered. "But please don't make a noise—the other guests—"

BANG!

Dan's powerful shoulder had already struck the door panel with tremendous force. The wood cracked and shivered.

Again and again Dan's shoulder made a living battering-ram, which no ordinary wood and brass could withstand. At the last and most terrific blow, the door was wrenched loose from lock and hinges, and crashed inward upon the carpeted floor, as Dan Dunn leaped over it.

The next instant Dan was crouched over the prone body of Judge Borland, with the frightened manager trembling at his shoulder.

"Shot! He's dead. Don't touch a thing here hut go phone the police!" Dan's words came short and swift, inspiring obedience.

The manager fled from the room, only too glad to get away from the sight of murder. Dan, meanwhile, searched the room for possible clues. He had just finished when heavy steps in the hall announced the arrival of uniformed officers of the law upon the scene.

"Hello, Dan!" cried the blue-coated sergeant as he stepped over the broken door. "You beat us to the job in your old-time style again, I see. Huh! What's this we have—another murder?"

Dan threw him a shrewd glance.

"You can call it that if you want to, Sergeant," he smiled. "I've been going over the situation while we waited for you. That window, for instance. The murderer left damp footprints on the sill coming in, but he didn't go out that way. I Damp Footprints on the Windowsill found the window locked on the inside. The footprints are the only traces left on the window. I've been over it with a glass looking for fingerprints; but there aren't any. You can see for yourself, Sergeant. Take this magnifying glass and look closely.''

"I'll take your word for it at the moment, Dan. Excuse me while I make a brief examination of the body. After that I'd like to ask you some questions."

"You'll find, if I'm not mistaken, that it's a funny case," Dan told the officer a few moments later. "You see, the murderer ought to have been here when I broke clown the door. Only, he wasn't! And that is going to give you something to chew on."

"What on earth do you mean?" muttered the sergeant, bewildered.

"Just this," replied Dan swiftly. "The door was locked, also from the inside, with the key in the keyhole. So what can we think? The murderer could not have escaped through the transom, because it is still closed, and the dust on it has not been disturbed," he said, and paused. "Hm-m-m! What's this—? I didn't notice it before!"

Dan had moved over toward the broken door. Now he whipped out a small pocket magnifying-glass. and bent over the lock, in which the key still remained. Then raising the door from the place where it lay into a brighter light, he studied it again. After a minute he straightened up, with the hint of a smile upon his lips.

"Sort of baffling, isn't it, boys?" he said.

The two officers were more than ready to agree. In fact, they said so plainly.

"It beats me, Dan," muttered the sergeant. "Both door and window were locked from inside. Yet, whatever man or woman may have shot the judge couldn't have just disappeared into thin air. I can't make head or tail out of it."

"The fact is, Sergeant," remarked Dan after a pause, "that whoever shot Judge Borland simply walked out through the door and locked it after him! Perfectly simple, once you understand it."

"But—but—from the inside?"

"Exactly!" Dan smiled. "The murderer locked it FROM THE INSIDE!"

The sergeant's face flushed red with puzzled anger.

"Then why wasn't he here when you broke in?" he shouted. "Dan, you've got my head going around in circles I I'll be nutty if you keep this up!"

"Me, too," grunted the other officer, leaning forward. "If you know the answer, Mr. Dunn, why not tell it to us, straight?"

"You missed those scratches on the key!" said Dan grimly.

CHAPTER TWO
The Crime Master

A quarter of an hour later, in the office of the Chief of Police, Dan Dunn proceeded to solve the problem of the locked door.

"It was really a clever trick the murderer used, Chief," he explained. "And if I hadn't discovered those tiny scratches on, or perhaps I should say INSIDE, the eye of the key, I might have been as much mystified as yourself. You see, after shooting Judge Borland, the criminal locked the window from the inside, then opened the door and turned the key in the lock —like this—until the bolt was just ready to slide home. Then he placed a thin, short sliver of steel through the eye of the key. A strong, thin cord was attached to one end of the steel sliver, and then passed under the door so that it could be pulled from the outside. Look! I'll draw you a diagram, so you can see just how it worked... Next the murderer went out, closed the door, and simply pulled on the string. The key, in fact, was as easy to work as if he'd used his fingers on it. In turning, it let the steel sliver fall to the floor, whence it was drawn easily through the crack under the door. There remained only the microscopic scratches on the eye of the key to show how the criminal had escaped, and he counted on nobody ever discovering them."

"As simple as that!" breathed the Chief. "But here's another puzzle for you to solve. The bullet, though fired at close range, went only part way through Judge Borland's body. And yet NO BULLET COULD BE FOUND by the examining doctor. This office can't make head or tail of that fact. Can you, Dan? You're our only hope, now."

A swift smile of understanding crossed Dan's face.

"Yes!" he returned. "I think I can, Chief. Your not finding any bullet confirms a suspicion I had, when I first examined Judge Borland's body immediately after he was shot. I noted that he had been shot through the heart in such a way that he died instantly and shed almost no blood. Yet there was a WATERY SPOT ON HIS SHIRT, nearly invisible but real enough, all around the edge of the wound! Put those two facts together, and they tell just one story—Judge Borland was shot with an icicle!"

The Chief gasped.

"An icicle! What on earth do you mean? I don't get you at all!"

"I mean," said Dan Dunn, "a bullet-shaped piece of ice fitted into the pistol cartridge. Being light, it penetrated only part way through the victim's body; and being ice, it melted almost immediately and left a watery spot near the wound. The murderer probably kept it in a box of dry ice—like this. A little box that fitted the pocket."

Dan picked up a small paper box from the. Chief's desk.

The Chief's jaw snapped shut.

"Dan," he exclaimed, "you've found out the murderer! As luck would have it, my men reported a raid on the rooms of a suspected criminal just as you came into this office. They found a large-caliber pistol and a box of dry ice, in a drawer."

"That's luck!" barked Dan. "Much better luck than I had hoped for."

"The occupant of the rooms had fled," the Chief went on. "But we know his name. It is Ivan Eviloff... And now, I am going to introduce you to the Sergeant who made the raid!... Oh, Dennison!"

Seated at the Sergeant's desk, Dan Dunn examined the evidence found in the rooms of the mysterious suspect known as Ivan Eviloff. The pistol, equipped with a silencer, and the harmless-looking little paper box half filled with dry ice occupied but a moment's attention. More interesting, Dan found, was a certain paper covered with strangely assorted figures—numbers arranged in regular lines.

"This," muttered Dan, "is undoubtedly a message in a secret code, or rather, a cryptogram... Here's a number, 108, followed by a couple of smaller numbers—do you see?—by a Number 19, and then by a 3. I believe that means that we'll find the first word of the message is the third word in the nineteenth line of the one-hundredand-eighth page of a certain book used by the criminals. Let's hope it's a book that can be easily obtained ... I wonder, now—Sergeant! What's the easiest book for anybody to get his hands on, wherever he may happen to be, and to get hold of on short notice? That is, supposing he doesn't carry a copy on him?"

The officer thought a minute, frowning. "A dictionary?" he suggested. "Or perhaps a telephone book?"

"Guess again!" smiled Dan. "Telephone books would be too local."

"Well," replied the Sergeant, "the only other I can think of is a Bible—"

"Right the second time, Sergeant! Especially a Gideon Bible. Remember, there's one in every hotel room in the country; and I'm sure you have a copy here at the Police Station. Let's have it!"

The officer strode out of the room, and in less than a minute returned with a large, black-bound book. Dan smiled as he laid it open at Page 108, and drew a sheet of paper toward him.

"You know," he said, "if we can decode this message, it may possibly tell us something about the murderer's contacts, or his whereabouts. We'll see. You read off the numbers, Sergeant, while I look them up. Begin! This ought to take only a brief study."

At the end of half an hour, Dan Dunn rose to his feet with triumph in his eyes.

"Here, Sergeant," he said, "is the message, completely decoded. Read it through and tell me just what you think of it. The words are plain enough, and if it means what it says—"

Bending over Dan's translation, the officer read—

"Men and gold will be waiting for you at the place you know as soon as you have done the deed of revenge. They will fly you to our secret refuge. Trust him who hands you the black cowl. We salute you our new Master and place ourselves and resources at your command.

"Signed, THE CONQUERORS"

"Great guns!" whispered the Sergeant. "That ties Eviloff up with the murder, all right. But the trouble is that it shows lie's safe for the time being. He's escaped by plane to the unknown headquarters of some unknown but probably powerful gang—THE CONQUERORS, as they call themselves. And we've absolutely no clue as to where that headquarters may be. Mr. Dunn, it's up to you to help us discover it! This is likely to be the biggest job yet, unless it's a hoax."

Meanwhile, hidden in the tropical Caribbean Sea, is an isolated island whose steep-walled sides and rock-infested coastline forbid exploration from the sea, and make hazardous even the cautious approach of steam or sailing vessels. There, behind a screen of jungle trees, a small army of men hurried to their sinister tasks at the orders of their newly chosen master, the murderer, Ivan Eviloff.

In the great power-house of the Conquerors, buried deep beneath the surface of the jungle-covered island, the Master Mind, clothed in his disguising tunic and jet-black cowl, examined the mighty dynamos whose generated forces were to terrorize the entire world. A crop-headed attendant, in the uniform of the organization, followed him about from room to room. Wherever Eviloff turned the man was at his shoulder.

"Master," said the latter, in a hushed voice, "even yet we lesser minds cannot understand how you discovered this way of harnessing the surge of the ocean tides to provide you with limitless power. These machines—they are like nothing the mind of man has ever invented."

"Ah, yes, Skearge," interrupted Eviloff. "These machines do generate limitless power—power to control nations—power to bring the whole world to my feet, begging mercy! They are MY invention. And the secrets of their construction are known to no one but me."

"We can boast of helping you in a humbler way, Master!" replied the attendant. "As when our faithful spies employed themselves as sailors and took possession of certain ships carrying desired materials; and later brought those ships to this island. When the cargoes were unloaded they took the ships and the captive crews out to sea again, and sank both without delay. No single captive survived to tell the tale! The newspapers reported all the vessels lost at sea— nothing more."

"That is well!" exclaimed Eviloff, with a sharp gesture. "Our cause is worth the sacrifice of a thousand crews of stupid seamen. Even should a million perish, I, Ivan Eviloff, shall be the World's Master."

CHAPTER THREE
A World At Ransom

Hovering in the Conquerors' dirigible above a small, uninhabited islet some hundred miles from the gang's headquarters, Ivan Eviloff pointed dramatically out of the window of the control room.

"There," he said, pointing at the tiny spot of land below7 them, where the blue Caribbean waves dashed against a dazzling white beach, "is the target for our great expert ment."

The hard-faced navigating officer chuckled. "Have no fear, Master," he said. "With the power our huge generators have built up at the home powerhouse we can send a lightning bolt which will blast that island out of existence. No earthly matter can resist!"

Eviloff fingered the dials. Suddenly a jagged beam of light flashed downward. The sound of fifty thunderclaps detonated.

A cloud of pulverized earth and spray arose from the spot in the ocean where the island had been a moment before. Sea water boiled for a mile about the center of the explosion. Then gradually the muddy cloud settled, to reveal nothing except yellow, lashing waves.

Eviloff turned with a triumphant hiss.

"It is success!" he cried. "With this man-made lightning, I am allpowerful. With this terrible weapon I am master of the world's fate."

The navigating officer bowed deeply in assent.

"I never doubted it, Master!" he exclaimed. "And now, what are your further commands?"

Ivan Eviloff favored the officer with a look of approval.

"I predict," he remarked, "that you will rise very high in my organization, Captain. And now we head for the home island."

"We shall arrive in half an hour!" replied the man, smiling.

As the giant dirigible landed, an eager crowd of helpers rushed out to tow it into its camouflaged hangar. But the Crime Master did not wait to descend from the gondola in the ordinary way. After swinging rapidly down a rope ladder, he set off at a swift walk, to be greeted by his faithful subordinate, Skearge, who had appeared from the direction of the offices.

"I never doubted your success, Master. It is indeed wonderful," cried the latter.

Eviloff nodded, but did not slacken his pace.

"We go to the office immediately," he stated. "The time has come to announce our authority publicly. Get me pen and paper without delay."

"Yes, Master," answered Skearge. "They are waiting you up on your desk. Is there thing else you desire?"

A quarter of an hour later, Eviloff handed a boldly written manuscript to his faithful attendant with the brief remark, "You may read it—my first public decree! Only a small beginning, but there will be others-

"'To the Federal Bank—'" Skearge read in an awed tone. "'You wju provide our agent with one million dollars in gold bullion and see him safely aboard his plane. The plane is not to be followed or interfered with in any respect. If these instructions are not followed exactly, your bank and one square mile of the city around it will be completely destroyed by means which you cannot possibly prevent. Signed 'The World Master.'"

"They will not dare refuse," murmured Skearge respectfully.

"If they do, my threat will be carried out to the letter. They shat learn not to disobey, for I shat punish with completeness and dispatch," snarled Eviloff. "Now go. Skearge, and take this message to the racing pilot, who is even now waiting for it at the hangars. He knows where and how it is to be delivered."

Barely an hour had passed before the Conquerors' swift plane raised the coast of America, and circled to land near a remote and deserted section of beach. No human dwelling was within sight. No ship or sail-boat showed inside the horizon. No road marked the land.

So skilful was the pilot, and so well did he know that particular part of the beach, that he was able to taxi his seaplane into water shallow enough for him to wade ashore at a point where a battered but powerful-looking car stood among the sand dunes. The driver of the car was waiting, his hat pulled low and his coat collar turned up about his face.

"Give the pass-word!" he barked as the pilot splashed ashore, without removing the disguising goggles and helmet.

A drawn pistol and the words "Skull and bones" seemed to satisfy the watcher, who thrust out his hand for the letter the pilot produced from a watertight pocket.

The car's driver pocketed the envelope and growled, "You have a verbal message too, I suppose? Let's have it quickly."

"Only this," replied the pilot drawing a second letter from his pocket. "The Master sends you instructions in this second envelope concerning the delivery of his message which you have just receive Let nothing interfere with your carrying them out, if you value your life. The Conquerors do not forgive mistakes—or make them!

"I'll make none!" answered the other, harshly. "The instructions will be followed."

He remained standing in his tracks until the plane had taken of again from the shallow water and winged away into the east. Then he turned back to his car, muttering under his breath, as he walked.

"There goes one man who has seen the Master. Not one of us on this side of the Atlantic knows where his real headquarters are. We couldn't possibly betray him if we wanted to. He trusts us just so far!"

Stepping to the front of the car he drew the second envelope from his pocket and opened it.

"Now for the instructions... Let's see... This says that Pm to post the message in New York City with the least possible delay. That is five hundred miles from here—which means I must charter a plane at the nearest air field and fly all night. Expense is never a consideration with the Conquerors. Anyhow, there's no time to lose, for the Master treats delay almost as severely as failure."

Eviloff's messenger was able at short notice to secure a large two-motored cabin plane, for which he paid a liberal charter fee out of the ample funds entrusted to him by the Conquerors; and, a little before dawn, his ship roared above the roofs of sleeping farms on the city's outskirts. After that it was but moments before he circled Newark and prepared to land. From there ordinary transportation took the messenger to the downtown section of New York, where he slipped the letter into a corner mailbox and hurried away in the pale light of early morning. His mission was accomplished.

The noon mail brought to the offices of a great New York bank the letter which had been written less than twenty hours before by Ivan Eviloff on the secret island of the Caribbean. The clerk who opened the letter shook his head as he read it.

"Hmm," he mused, "another crank letter. The bird who writes this says we must deliver him a million or he will destroy the bank. Huh! Guess I'd better show this to the President anyhow. I won't take the responsibility of handling it. I might be destroying evidence."

He stepped quickly through the door of a private office, and handed the letter to a lean-faced man seated at the mahogany desk.

"Mr. Bond," he began, "here is an extortion letter I thought you ought to see, because it threatens damage to the bank building. I suppose there's nothing to the threat, but, as a matter of form. I thought you alone should deal with it. It may be a pure hoax—"

"I'll be the judge of that, Collins," the President interrupted. "You did right in bringing it to me... Hmmm. Clearly a maniac wrote this. He threatens to destroy the bank and do a lot of other damage if we don't furnish the money. Well, turn this over to the police... usual procedure. Every bank gets a number of such threats but of course there is almost never any attempt to carry them out. When any one of them looks especially vicious, we give it to the police."

In response to the bank's telephone call, an officer appeared and received Eviloff's extortion note. After reading it, he smiled reassuringly to the clerk.

"We'd better make up a dummy package of lead bars," he decided, "and leave it with a detective in your cashier's office, just in case this crank shows up. You never can tell. Not that he's likely to, you understand—but just in case!"

That very afternoon, however, the Crime Master's agent did show up. He came stealthily, a man of ordinary appearance, disguised only by a mustache; and, peering in a side window of the bank, recognized the police detective on duty in the cashier's office. Instantly he drew back, made his way to the street, and proceeded to lose himself in the crowd.

CHAPTER FOUR
A Threat Fulfilled

The agent lost no time in presenting himself at the district headquarters of the Conquerors and reporting the bank's attempt to set the police on their trail, instead of giving up the gold bullion.

"I dared not do more than observe the trap set for us," he told his criminal chief. "My capture would have accomplished nothing for us, and might have caused some of the comrades to be traced through me."

"I will transmit your report by wireless to the Master's headquarters," replied the other. "So far as I can see you did rightly, comrade; but it is not for me to decide. You must not leave the city until we receive the Master's reply. Obedience is the Conquerors' first law!"

"I go now," said the agent. "But I will return shortly for further instructions. I obey the Master! Transmit my report at once!"

On the secret island, Skearge rushed into the Master's presence with a copy of the radio message in his hand. His face told Eviloff the news as plainly as any written words, before he had crossed the room.

"Ha!" barked the master criminal, his face writhing with passion. "They refused my demands, eh? They will regret it! Let me see the message!... So! The fools not only refused to deliver the gold, but set a stupid trap for my agent. A trap he avoided, of course. He is a clever agent, and you may commend him in your reply. As for the Bank—I'll teach them to refuse me! Heh! Heh! Quickly now—order the dirigible prepared for immediate flight. Tell the power-room engineers to make ready their maximum charge of destroying lightning. We take off at once for New York City, arriving during the night hours. You, Skearge, I leave in temporary command of the Island, but I shall keep constantly in touch. Now, make haste! You have much to do!"

"At once, Master!" answered the faithful Skearge, as he hurried from the room, to give the necessary orders.

Within an hour the giant airship crept out of its camouflaged hangar as many assistants threw their weight on the ground lines; and barely was it clear when a car rushed up to position beneath the lighted gondola. From it Ivan Eviloff emerged, and climbed the ladder alone—for the crew of the ship were already aboard and at their stations.

"Cast off!" came the cry from the control-room; and the ground crew released the lines which had held the huge air-monster earthbound.

The ship rose into the evening sky, heading swiftly northwestward.

Rapidly the Master made his rounds of the control and engine rooms, checking each detail with expert knowledge. None knew so much as he of the mighty motors t which drove the dirigible—for had he not invented them himself? The inspection finished, he turned to the captain of the ship.

"Have you any report?" he demanded, his eyes gleaming.

"Yes, Master! Weather reports indicate no high winds, but continued cloudiness ahead. Standing out from the coast, we may fly above the ceiling at full speed and risk no discovery until over the city."

"How many hours should the trip take us at our greatest speed?"

"Only five, Master, unless we run into unexpected winds. We are faster than any other dirigible ever flown. Moreover, our motors are noiseless, so that we can hover over the city at any height—even descend to touch the housetops!"

So, for five silent hours, the deadly airship swam forward above the clouds on its mission of destruction, a monstrous shark of fthe air. At their posts within the control room, uniformed mechanics and navigators steadily pursued their tasks. Quietly watching their gauges, the engineers performed their routine duties...

Eviloff paced the control room impatiently muttering to himself.

At eleven p.m. the captain approached Eviloff and saluted.

"Master," he reported, "we are now passing above Staten Island, at an elevation of five thousand feet. The cloud-bank extends down to about two thousand according to our rough calculations. We are reducing speed to hover over Lower Manhattan. We await your orders before proceeding further."

Eviloff nodded impatiently. His thin lips twisted into a snarl.

"Prepare to lower an observer, and meanwhile descend to the lowest limits of the cloud ceiling. When the observer's basket swings above the Battery, let me know. From there on we go carefully at low speed."

The officer saluted again and turned to a crew who stood over an open trap door in the floor of the control room.

"Prepare to lower away!" he snapped.

Below the opening swung a stout basket, containing a man. A brave man indeed to make that terrifying descent from the clouds!

Like a great fish diving to the ocean depths, the dirigible swam downward until almost below the thick clouds which wrapped the unsuspecting city. Then the windlass crew released the drum, the rope paid out, the basket with its lone observer dropped swiftly until it dangled just above the skyscraper roofs—dangled like a tiny fly at the end of a long spider's web. Earphones hugged the observer's helmeted skull; night glasses were clamped to his eyes. Street by street, he reported by telephone the passage of the cloud-hidden airship toward its goal.

At last, ten blocks from the great bank building, the dirigible's motors stopped entirely, and the airship, still hidden in vapor, eighteen hundred feet above, nosed downward until its control-room appeared through the screening mists.

"Master!" the observer's voice came up from the dangling basket. "The bank building is dead ahead. In two minutes you will be directly over it."

"We hear and we see!" came the reply. "You will be raised to the ship immediately."

The basket began swinging in shorter and shorter arcs, as it rose rapidly toward the great belly of the airship; and a few seconds later rit disappeared through the open hatch.

Eviloff turned to the radio officer.

"You are in touch with Skearge at the home island?" he snapped. "He has built up full power in the generators? The giant batteries are charged? Eh? What does he say?"

The radio officer swung about with a worried face.

"He says two of the generators have burned out suddenly, but the batteries are almost completely charged."

"Malediction!" yelled Eviloff in fury. "We are left with only half power! But we will use that now, and destroy the bank at least."

He whirled around to face the mechanic at the special switchboard.

"Quickly! We are just over our target now. When I drop my arm, throw in the master-switch...

"Ready—For the punishment of my enemies—THROW!"

Sparks flew from the switchboard at the contact. A livid, forked flame shot down from the ship to the earth. A stunning explosion... Then the dirigible lifted silently into the dark clouds leaving death and ruin below.

The great airship, carrying the perpetrator of horror and bloodshed, was soon speeding southeastward, headed for its tropical base.

A telephone bell rang long and insistently in the office of the nation's Secret Service. The operative in attendance answered, and listened grim-faced while the New York police at the other end of the wire poured into his ear the first report of midnight disaster, following it with a demand that the best operatives of the department be put on the case. From that moment onward other telephone wires hummed.

Dan Dunn, Secret Operative 48, answered the call at his hotel room, and listened without speaking while his chief gave him a brief outline of the bank disaster.

"I get the picture, Chief," he replied... "Yes... Yes, I'll catch the first plane out of Dallas for New York... Yes, I'll be there, inside of twenty-four hours... All right, I'll report at police headquarters and go from there immediately to the scene of the explosion."

Dan's reckoning of the time necessary was accurate. The following evening he found himself on the street corner outside the ruined bank, gazing up at the wreckage.

"It looks as if the explosion had driven down from the top of the building," he observed. "And that would hardly be likely if it were an inside job."

"Yes," answered the sergeant who accompanied him. "That's just what bothers us. Even our experts can't figure how it happened, unless an airplane deliberately dropped a bomb on the building. But even at that, the wreckage is different from that which a bomb would leave. Besides, there are no traces of chemicals among the debris—such as a bomb would leave. One of our chemists said that if it were possible for such damage to be caused by lightning—and if there had been a thunder storm 'that night—he could have understood it."

Dan made no comments until he had reached the office of the New York Chief of Police; and there he asked for two papers—one, the official police report of the bank disaster; the other, the crank letter threatening the bank's destruction, received only a few hours before the actual happening.

Rapidly he perused the report, then turned his attention to the letter, his photographic eye taking in details that would be obscure to the ordinary intelligence.

A smile crossed the face of the police captain who was assigned to aid him.

"You won't find any connection between those two papers," he chuckled. "One's a report of competent officers, the other's just the ravings of a lunatic!"

Dan Dunn arose suddenly and kicked back his chair.

"Quick!—a telephone!" he snapped. "I've got something!"

Dan's first glance at the so-called "crank letter" had brought him a strange sense of familiarity. Somewhere, he felt, he had seen very similar handwriting—perhaps the same. And not long ago, either! Then, in a flash, the accurate memory of it had come ... He seized the instrument which the Captain pointed out on a nearby desk.

"Give me Police Headquarters, in Dallas!" he ordered tersely.

"Hello! Lieutenant Walsh?" he asked when the connection was made. "Dan Dunn, Secret Operative 48, speaking from New York headquarters. Wire me a photo of Eviloffs handwriting... Yes, a few lines and signature will be enough... You can have it here in two hours? Fine!"

Walsh was as good as his word, and within two hours, the New York Captain brought in the photograph of a message found in Eviloff's rooms and known to have been written by him. One glance at the two specimens, laid side by side, was enough to show their identity. The "crank letter" had certainly been written by Eviloff. Puzzled, nevertheless, the police captain stared at the sheets in Dan's grasp.

"But who—" he muttered. "Who is this Ivan Eviloff? This office has never mugged the bird!"

Briefly Dan explained:

"Eviloff, Captain, was at one time the foremost electrical wizard of Europe. But one of his large-scale experiments there resulted in such great loss of life that he was forbidden to carry on his tests. He came to this country, and rented a big laboratory in one or two western cities. But his assistants became so alarmed at his queer actions and ravings that they brought the matter to the attention of medical and police authorities. As a result, Eviloff was confined in an asylum for the insane, and while there he showed an intense hatred of all organized government. Within a year he escaped and is now being hunted as a crazed anarchist. Unfortunately the man has the quality of leadership and has evidently hooked up with a powerful band of international criminals, whom it has become our job to locate... I have an idea this 'crank letter' of his to the Bank may supply a clue to their whereabouts. At any rate, we can't afford to overlook a single possibility. Can you take me to your technical laboratory right away, Captain? I'll need to use a powerful microscope!"

Two minutes later, Dan was introduced to the Laboratory Chief, who gladly supplied his request.

Then, for half an hour, Dan examined the letter through powerful lenses, made scrapings with a fine scalpel, then more microscopic tests, and finally beckoned the Laboratory Chief.

"I've a request to make, Doctor," he smiled. "I'm very anxious to borrow this instrument of yours for an hour. You see, I want to consult another expert and get his opinion on something I've discovered... Captain, will you drive me across the city?"

Speeding up Riverside Drive in the fast Police car, the Captain ventured a question to the famous operative.

"You've given me the address of the party you want to see, Dan," he said. "But just who is he, anyhow? You said something about an expert—"

"Right, Captain," responded Dan. "An expert on different kinds of rocks and earth. He's a retired officer of the Geological Survey, who still runs a small private laboratory in the city. Cleverest man I know in his line, and he'll make a quick examination for me, without any fuss or red tape... Here we are! Park your car just opposite this building, Captain..."

"But who do you want to see him about, Dan?" insisted the still mystified officer. "What's rocks and earth got to do with Eviloff's crank letter and that microscope you're carrying?"

"You'll see in a minute," replied Dan, as he pressed the bell.

An elderly bespectacled gentleman met them outside the door of the little laboratory.

"Dan Dunn, of all that is strange!" he exclaimed, stretching forth a hand in welcome. "I was thinking about you only this morning! Tell me what I can do for you?... Come in! Come in!... Now, what is your business, Dan?"

Dan smiled cordially.

"Another little puzzle for you to solve, Colonel Wells. I have here a few grains of sand which I scraped off a sheet of letter paper. I want to know just what part of the world that sand came from. I have brought a microscope along from Police Headquarters so that you can make your examination at once. The business is pretty urgent."

Quickly Colonel Wells adjusted the lenses over the glass slide on which Dan had fixed the telltale grains of silica.

"Hmm! Very odd indeed," he muttered. "Just a moment while I consult my library."

In ten minutes the old Colonel returned with a sheet of notes.

"This is certainly interesting!" he exclaimed. "These grains of 208 DAN DUNN sand are evidently tiny bits of coral peculiar to a certain group of islands in the Caribbean Sea. I don't know what that may mean to you Dan, but there are the facts."

"It means plenty, Colonel, and thanks a million for your prompt work!... Let's go, Captain!"

Dan turned to the police officer.

"What on earth DOES it mean Dan?" the latter asked as they left the laboratory office. "I have a vague idea, but—"

"Just this Captain—Eviloff's note was clearly written and sent from some island in the Caribbean—a coral island certainly, and probably an uninhabitated one. There is one more line by which , we can check this. And that is the watermark on the paper. Right now I want to go back to headquarters and do some telephoning."

Back at the police office Dan consulted a telephone directory, then lifted the receiver, "Whitfields Stationary Company?" he asked. "Police Headquarters speaking ... Will you please tell me what branches you have in the neighborhood of Cuba or the southern states ... Yes, yes! I'll hold the line."

"Hello... what is that? Your only southern branch is in Jacksonville, Florida? No branches in Cuba or anywhere outside the states... Right! Many thanks!

"Chief!" said Dan, turning from the telephone to the white-haired officer at his side, that completes our circumstantial evidence that Eviloff has his headquarters in the Caribbean—probably on some uninhabited, small island of coral formation."

"Splendid!" cried the officer. "I shall communicate with Federal Headquarters so that an immediate search can be started. Thanks to you Dan, these birds are going to be easy meat for us from now on!"

"Not so easy perhaps!" Dan said. "Remember this Eviloff isn't Mary's little lamb, and catching him is apt to be dangerous. I am convinced that he is in possession of one of the most terrible electrical weapons ever invented by the mind of man—the same weapon which destroyed the bank in this city only a few days ago. And then, there is his gang of armed anarchists!"

"You're right, Dan—and thanks for the warning!" cried the officer.

CHAPTER FIVE
The Second Threat

Seated before an expensive radio outfit in his office on the Secret Island, Ivan Eviloff listened to the reports of his latest coup.

"Another police report," came the announcer's voice, "indicates that the Federal Bank was destroyed by an electrical discharge. Lightning is the only explanation possible, incredible as it may seem; and all rumors to the contrary are false!"

"Ah-ha!" snarled the Crime Master, turning to Skearge, who stood in attendance. "The stupid police are completely baffled. Too completely. Do you see, Skearge, they do not even connect the destruction of the bank with my message of demand and warning? That must be remedied at once!"

"Ah, yes, Master!" responded the crop-headed man. "You mean that you must prove to those fools that the bank affair was no accident of nature, but your deliberate punishment for their disobedience?"

"Exactly!" gritted Eviloff. "The time is now ripe to send another message which even those thickheads must understand!"

"What shall you tell them this time, Master?" asked Skearge.

"I shall demand," shouted Eviloff, "that the states of New York and Texas release the inmates of their prisons and escort them safely aboard ships in which we shall bring them to the Secret Island. If the stupid authorities refuse this demand also, those same prisons will be destroyed!

"But, Master, what will you do with all those released prisoners?"

"We need additions to our forces Skearge. And what better men for our purpose than those who are the enemies of government?"

Eviloff's second letter was dispatched by plane and special messenger in the same way as the first. But meanwhile Dan Dunn, Secret Operative 48, had arrived at the Government Naval Base in Florida on the trail of the madman's gang.

Bending over the dials of a shortwave radio, he had been seeking for several hours to pick up the code messages which he suspected Eviloff's organization would be sending to and from their island headquarters.

Dan's luck was with him. On four separate occasions he picked up signals on a very short wave, which proved to be in a code of numbers similar to that found in Eviloff's room in Dallas. These messages he took down in pencil and later decoded easily. There was no mistake. Two of the messages were clearly from the Crime Master and two were replies, probably from the mainland.

Dan grunted with satisfaction as he bent over the copy.

"We have them now!" he exulted. "Only let them keep on sending code on that wave length and we'll have their headquarters located exactly within a couple of hours. Criminals always make a slip sometime and they have made one now. Electrical wizard he may be, but Eviloff seems to have forgotten that there are such things as radio direction-finders. I'll speak to the commander of the Naval Base at once!"

In the Naval Commander's office Dan Dunn came quickly to the point.

"I've intercepted four of the gang's messages," he told the officer. "Two of them I believe were sent from a small island in the Caribbean—possibly one of the Bahamas group. Those are the ones I am interested in chiefly; but you might as well locate the land station or stations at the same time. How soon can you get your direction-finders onto their wave length?"

"I'll do that immediately, Dan," answered the commander. "We'll get cross bearings from this base and from New York, and where the lines cross on the map will be exactly the spot from which your radio signals come. By the way Dan, is this going to establish a new method of crime detection?"

"Hardly new, Commander," replied Dan with a smile. "The Secret Service has worked it before, but never I think where so many human lives hung on the results. This Eviloff is not only a madman but is possessed of far greater power in weapons and organization and far greater cunning in his own crazy brains than any other gang leader in history."

The officer nodded soberly.

"I shouldn't be surprised, Dan. Have you formed any theory as to the precise means by which he managed to destroy the Federal Bank, and proposes to strike at the two States' Prisons?"

"Yes," said Dan, "I have! Though of course no theory is absolutely certain. I believe that Eviloff's lightning apparatus was operated from a dirigible airship. An airplane would have been heard, and besides no airplane could carry the weight of such a powerful apparatus as must have been used. Now if you will allow me to use your telephone, I'll get the direction-finders to work on that special wave length."

"Go to it, Dan!" replied the Naval Officer. "We'll wait here for their reply."

Half an hour later the telephone in the commander's office rang sharply.

"I wonder now!" cried the officer turning to the instrument. "If 1 they have located your code station already, Dan, we sure are in luck! Hello—hello... What! you've picked them up already? And you've got the New York cross bearings too? Fine work men! We'll be right down and check up with you on the next code message that comes through!"

"I'll get my maps, Dan," he added turning to the Operative. "And if luck is with us again we'll have your gang located beyond the possibility of doubt. We'll go down now to the radio room..."

Their wait in the radio office was even shorter than they had expected. Eviloff's gang seemed to be keeping up a very regular radio correspondence between their headquarters and various local points in the United States. Two more messages came through from the Secret Island within the next three quarters of an hour and were duly plotted on a large-scale naval chart. The lines coincided, in both cases at a point in the Caribbean 1 Sea not far from the Bahamas. But, amazingly enough, no point of land marked the blue expanse of sea on the map at this spot.

"What do you make of that, Dan?" asked the commander with a puzzled frown.

"It doesn't surprise me in the least, Commander," Dan answered. "I fully expected that Eviloff would have picked out some tiny island too small or too recently formed to be on any map. Probably that little spot of land lies very low to the water and can't be seen for more than a few miles in the best of weather. Possibly, too, there are so many reefs and shoals surrounding it that ordinary ships would steer clear of it. The main thing is, we've got the place located. Our next job, with your permission, is to send out a scout plane to find out just what we are up against on that island of crime."

"Right you are, Dan!" cried the Naval Officer heartily. "I'll have a plane made ready at once! Orderly!"

A sailor on duty answered the commander's call and saluted briskly. The officer gave swift instructions.

"Orderly, present my compliments to Flight Commander Billings and say that I wish to have a fast combat plane prepared for immediate flight. Take on gas for a total trip of a thousand miles. I wish the best pilot to fly the plane with Mr. Dunn, as observer. Load extra machine-gun ammunition, six light bombs, and food provisions for three days. Also life belts in addition to regular parachute equipment. The pilot will fly under sealed orders and obey without question the orders of Mr. Dunn."

Dan turned to the officer with a quick smile of appreciation.

"Thank you, Commander, for your prompt and excellent co-operation ! If we are successful in foiling the plots of this mad genius Eviloff, thanks will be due largely to your intelligent help!"

"That's all very well, Dan," answered the Commander. "But your safe return will be more than enough reward for me! You're going into deadly danger, man! Of course, I realize that it is necessary..."

So efficient were Uncle Sam's mechanics that the plane was provisioned and ready inside of thirty minutes. Dan Dunn, clothed in aviator's flying suit and helmet, climbed into the rear cockpit behind the ace pilot of the naval base, and the machine took the air with a roar. Dan gave the compass bearings from the data he had memorized.

Fortunately the weather was clear for the great part of the trip, and just before sunset they approached the blank spot on the map where the island was supposed to be.

After scanning the horizon on all sides the pilot turned a gloomy face to Dan.

"I don't see a sign of an island, sir," he observed. "Only clouds!''

"Clouds are a lot better than nothing, pilot," Dan answered. "If you look more closely at that bank of clouds over to the east I think you will see something more substantial underneath them. How about it?"

The pilot flew for some minutes toward the looming cloud bank before he turned again with a sheepish smile on his face.

"By Jove, sir!" he exclaimed. "You certainly have keen eyes! There IS an island there, lying low to the water! I can see the cliffs now rising about a hundred feet above sea level. What do you want me to do now?"

Dan pulled a pair of binoculars from his flying suit and peered at the little spot of land for a long moment.

"That's our island all right. Lieutenant!" he stated. "But there is no use trying to make observations now—it will be dark in fifteen minutes. The sea is calm tonight, fortunately, so we will just set clown on our pontoons and ride it out until daylight."

The night passed uneventfully, and at the crack of dawn they took off, circling the tiny island at 3000 feet.

At first only a thick fringe of jungle was visible; but as the plane swung high over the interior, Dan Dunn pressed his binoculars to his ! eyes with a sharp ejaculation.

At the same instant Skearge rushed into Eviloff's private office with a shout of wild excitement.

"Master! Master!" he cried. "A strange air plane is circling ovei the island! What shall we do? It must be an enemy! No plane of ours is due—"

"What!" yelled Eviloff, his features contorting with rage. "Break out the anti-air craft machine guns!—that plane must not get away! Our secret refuge must never be revealed to our enemies. Quick! Tell the gunners to give no quarter! They must destroy that plane and its occupants without fail—Hurry!"

But Skearge was already on his way.

With the speed and discipline of well-drilled soldiers, Eviloffs minions set up their deadly weapons on the landing field outside the Crime Master's Headquarters. Swiftly the lean black muzzles were pointed skyward and trained upon the Government plane.

CHAPTER SIX
Shot Down

"It's the Island we've been looking for, Lieutenant!" cried Dan Dunn, as the plane roared over the power house and central buildings of the island. "There's no mistaking it! Fly low so that we can see everything—''

But, instead of sinking lower toward the center of the island, the pilot suddenly zoomed his ship, as tiny spots of daylight began to appear in the fabric of the wings of the fuselage.

"Bullets!" yelled Dan, as he caught the significance of those suddenly appearing holes and the pilot's quick dodge into the sky. "You're perfectly right, Lieutenant! No use risking our lives, now they've discovered us. They have all the advantage!"

"We've seen a good deal anyway, sir," answered the pilot. "Shall I head for home?"

"Best thing you can do, Lieutenant. I only hope none of their bullets have reached a vital part of our plane!"

"We'll know in the next three or four minutes," answered the aviator. "I'm a bit worried about our gas tank. This plane is not so well protected as the heavy bombers. Wait a minute! Yes, sir, that's what I was afraid of—the motor's dying out! Best thing we can do is to set down on the water in a hurry before the heat of the motor sets fire to the leaking gasoline."

"Right again, Lieutenant!" Dan nodded grimly. "We'll be at the mercy of those devil's on the island once we're out of the air, but I guess there's no help for it. We'll have to take our chances. If only I had been quicker to see those machine guns down below—"

"Don't blame yourself, sir! I was a pilot during the World War in France, and I should have seen those guns myself in time to get away—even though they were camouflaged by the trees!"

Its motor dead, the little combat plane sank lower toward the rolling swells of the Caribbean, and in a few minutes was coasting over the wave crests to a smooth, if untimely, landing.

"Lucky for us, sir, that the weather's calm. If it were a storm we'd landed in, we'd crack up in a few minutes... There! Now that I don't have to bother about the controls I'll just tap out a radio message to the home base, telling our situation, and asking for help just as soon as they can send a squadron to pull us out of this mess!"

"And let's hope they make it fast," agreed Dan, gazing backward at the Island of Crime. "If I'm not mistaken, Eviloff is planning now to settle our hash; and, to be honest, I think he's got every chance of succeeding before help can possibly arrive."

"We'll sell our lives dearly anyway!" glutted the officer. "That little machine-gun stunt can work both ways, you know, sir. And we've got two guns right here in the plane, with enough ammunition to stand a siege!"

But Dan Dunn shook his head.

"Don't kid yourself, Lieutenant!" he warned. "Eviloff's gang will probably guess that we are armed and take no more chances than they have to. You know they can fly above us all day if they want to at high speed and drop bombs until one of them hits the target. And if that fails they can use their lightning machine just as they did on the bank. No, Lieutenant," Dan concluded bitterly, "we stand just about as much chance as a couple of celluloid cats being chased by a couple of asbestos dogs through a super-heated furnace."

"You can't scare me, sir!" responded the pilot with a carefree laugh. "I've tickled Death's whiskers so many times during the Big Show over in France that I don't worry any more. If our number is up, there's no use crying about it. And if it isn't, not all the Eviloffs in the Seven Seas can harm a hair of my head!"

Meantime, at his own Island Headquarters, Eviloff danced with fury and disappointment at the failure of his gunners to bring the Navy plane down immediately.

"Line those fools up in a row!" he shrieked, "and mow them down with their own guns! Those idiots' rotten shooting has betrayed us— and the fate of traitors is death!"

"But, Master," cried Skearge, "I pray you look once more. The Navy plane is down on the water five miles out from shore and almost invisible, but it is there! The gunners must have reached some vital part of the plane with their bullets, but the pilot and his observer are still alive."

''So!" snarled the Master Criminal. "We must reach them quickly. Probably they have already radioed their position to Naval Headquarters and we shall soon have a flock of fighting planes on our necks. Order out our best pursuit plane and pilot immediately. I will speak to the pilot myself."

Two minutes later a hard-faced man in pilot's uniform reported outside Eviloff's private office and saluted respectfully. The Crime Master turned upon him with tigerish ferocity.

"Get out your plane immediately!" he howled. 'Till every available space with high explosive bombs and see that you utterly destroy those two fools who dared to spy upon us in the aircraft of a hated government."

"Immediately, Master," responded the gangster, and departed on the run for the seaplane hangar, which was cut, cave fashion, into the cliff wall of the island.

Moments only intervened before a black, low-winged monoplane roared out over the water in the direction of the wrecked Government plane. As throbbing engines gave warning of the enemy's approach, Dan Dunn seized his binoculars and gazed briefly at the oncoming menace.

"Well, Lieutenant," he remarked calmly, "this is certainly where we find out if our numbers are up, as you put it. Unless I'm mistaken, that plane has been sent from the island to finish us off."

"You've guessed it, sir," the officer agreed quietly. "That's not a Navy plane; so it must be Eviloff's, and he's not planning to use machine guns on us. Flying too high and fast for that... Hold hard— he's just laid an egg and it's going to hit mighty close to us!"

With a wailing scream of tortured air the deadly missile hurtled downward—and the next second exploded almost aboard the wrecked plane. A huge fountain of water towered upward, hiding everything in white spray; and when it had settled, only two broken wing tips projected from the water at the point where Dan Dunn and the gallant pilot had so calmly awaited their fate.

Stunned by the explosion, their bodies sank limply below the waves. But instinct had caused Dan to hold his breath at the instant the bomb struck. His splendid vitality did the rest—and in a matter of seconds he had recovered his senses enough to struggle upward to the surface.

Gulping fresh air into his lungs, he quickly recovered full consciousness; and with the first returning strength in his limbs, started swimming in a wide circle on a chance of finding his companion in disaster. At last he saw the shiny wet top of a leather helmet shining above the water, and with a few powerful strokes, had reached and seized the body of the unconscious Lieutenant.

Even then his efforts would have been wasted, and both men would Seized the Unconscious Lieutenant have been drowned inevitably, had not Dan sighted at fifty yards distance the floating pontoon of the wrecked seaplane. With his last reserve of strength, Dan dragged himself and his still unconscious companion aboard the smooth-surfaced float—and almost collapsed. Gradually, as strength returned, he gazed about over the blank surface of the water in almost hopeless search of other useful wreckage.

But once again Luck came to the assistance of the great detective. Floating almost within arm's reach was a black metal cylinder which Dan recognized at once. It was a can of distress flares which had been attached loosely to the cockpit of the wrecked plane. Leaning far over the pontoon, he rescued the precious article and placed it beside him. Then he turned his attention to the half-drowned, unconscious Lieutenant.

Vigorous first-aid methods forced the water from the pilot's lungs, and brought a touch of natural color into his deathly white face, but his eyes remained closed, even though slow and labored breaths came finally through his nostrils. Dan shook his head sadly, as he rested beside his friend's body, and muttered:

"—Must have been hit on the head by a piece of wreckage, poor fellow. If we don't get help soon, he's a goner. It may take hours yet for any rescue planes to reach us —if they ever do!"

At that moment, however, the flight commander from the Florida Naval Base was in the act of dispatching a second squadron of fliers to search for the missing men.

CHAPTER SEVEN
Rescue

The sun was sinking toward a dark horizon as the first squadron of naval searching planes drew near the secret island off the coast of which floated the pontoon bearing Dan Dunn and his fellow castaway. Owing to the warm weather and calm seas, neither of them had suffered greatly from exposure. The lieutenant, however, had not regained consciousness.

While the squadron was still some miles from the end of its search tropical darkness shut clown over the water. Vainly Dan Dunn stared at the sun's vanishing rim in hope of seeing the silhouette of rescuing wings against the light. Meanwhile, a debate was going on by radio telephone between the flight commander of the rescuing ships and his officers. Many of the latter wished to set down on the water at a safe distance from the island and ride out the hours of darkness.

But the commander insisted that the first attempt to find the missing men should be done by searchlight without further delay.

"Their chances of staying afloat are getting less with every hour," he declared.

Dan's hopes had sunk with the sun, but they had not entirely disappeared. As the hours of darkness passed he strained his ears constantly for the sound of approaching motors. For, once he heard them, there was no chance of their passing them by providing they were friendly. He still had the case of distress flares he had salvaged from the water. And matches in a waterproof box!

Little by little a pale moon rose above the black ocean, and in the cold wind that had sprung up he shivered in spite of his heavy flying suit. Higher waves began to lap against the sides of the wrecked pontoon.

"Poor Lieutenant," Dan murmured, kneeling beside the still unconscious officer. "If help doesn't come pretty quick he won't be able to live through this cold and wet in his condition. If only—say! What's that? Am I dreaming or just imagining things? Seems to me I heard—YES! I did hear it. Airplanes coming from the west."

Moments later the welcome shape of a navy pursuit plane sailed between the pale moon and Dan's line of vision. Then another—and another—and another! Dan raised a faint cheer, though there was none to hear him.

"Hurrah for Uncle Sam's Navy! I might have known they would have been on the job. I'll light a flare now—they can't fail to see it at this distance ... If only my hands weren't so stiff—and here's hoping I don't drop the matches into the water!"

But Dan's luck still held good. The first match he struck burned in the shelter of his cupped palm until the flare sputtered into life. Rising as high as he dared on the frail pontoon Dan waved it above his head.

Almost immediately lights flared from the leading airplane, and the entire squadron banked on whistling wings to drive straight toward the spot where the flare glowed.

Just in time the first plane landed close to the cataways' position. For the waves were coming up much higher now, and even Dan Dunn's splendid strength was almost gone. Swiftly but gently the officers of the rescue plane lifted the two limp bodies from the water and stowed them away in the cockpits, wrapped in warm blankets.

"All right, boys," the flight leader called into his radiophone, 'Tm heading back at once to the mainland with Dan and the Lieutenant. They are both unconscious and we have to get them to a doctor at once. All planes will follow me back to the home base. We'll do no more scouting of the island until we get Dan Dunn's whole report. Those are my orders from naval headquarters."

Meanwhile a conference of great importance was going on in Eviloff's office, between the Crime Master and his faithful assistant Skearge. The latter was urging a change in the plans for terrorism which Eviloff had conceived.

''Master, now that the naval authorities have discovered our island we are in a position of real danger on which we had not counted."

"What do you mean?" snarled the black-cowled leader. "Have we not destroyed those wretched spies along with their plane?"

"I'm not so sure, Master," Skearge returned. "A few minutes ago one of our lookouts reported a strange light out on the water about five miles from the island. The light disappeared after a short time; but the thought occurred to me that at least one of the spies might have managed to stay afloat on some part of the wreckage. That light our lookout saw might have been the spy signaling another plane with a flare!"

"Impossible!" cried Eviloff. "How could any other plane—"

"Remember, Master," Skearge interrupted. "After the spies were shot down they had time to radio their position before we destroyed their plane with a bomb... Now my thought was this, Master—that before we antagonize the American Government any further, we strengthen our position by enlisting the outlawed men of other nations."

"Explain yourself!" exclaimed Eviloff, dropping into a chair beside his desk.

"Yes, Master!" Skearge continued. "I think that what we need is a special agent well known to the outlaws of the world, and particularly to those of oriental nations!"

"Have you anyone in mind?" demanded Eviloff, his eyes glittering with sudden interest.

"Yes, I have that," Skearge answered quickly. "Wu Fang, the internationally known criminal genius, whom that sharp Secret Service man, Dan Dunn, put into State's Prison some months ago. We could get him released, Master—"

"Good!" exclaimed Eviloff. "Make arrangements for it at once! You can reach our local agent by radio on the ultra-short wave we use. We must act quickly!"

Skearge wasted no time in carrying out these orders. Calling the local representative of the gang, his instructions were brief and to the point.

"You will proceed immediately to free Wu Fang and report to this headquarters the moment you have succeeded."

At the local gang headquarters three mobsters heard Skearge's words with alarm and excitement. "That is not going to be an easy job, comrades!" spoke their leader.

"Maybe so," grunted another of the trio. "But we have got to do it, if we value our necks."

And so it was that a certain visitor applied at the Prison Warden's office for permission to see Wu Fang during the visitors' hour. There was no reason why the permission should not be granted, so far as the Warden could see. The visitors interviewed their prisoner friends through a steel-mesh grating and under the watchful eyes of armed guards. Furthermore, escape from this particular prison was considered impossible.

The prison authorities, however, had not taken into consideration the cleverness of the gang the Crime Master had at his command. In a secret code language known only to a few of the cleverest criminals in the world, the visitor spoke to Wu Fang, giving him instructions to watch for an airplane flying over the prison yard at a certain hour and clay when the prisoners were taking exercise out of doors. Wu Fang signaled his understanding of the plot and his promise to be ready.

Two days later an autogyro with two seats and great lifting capacity hovered leisurely over the walled and guarded prison buildings, at an hour when Wu Fang's group of prisoners took their airing. In the hands of a masked man in the rear seat was a long coil of thin, stout rope, looped and weighted at one end. Unexpectedly the autogyro dropped almost vertically over the prison yard until its wheels were barely fifty feet above the high walls. Immediately the looped rope fell with uncanny precision until its uncoiled length stretched clear from the yard to the fuselage of the flying machine.

Instantly Wu Fang slipped the loop about his body and waved a signal, at which the autogyro rose suddenly in the air, bearing the prisoner with it. As he swept skyward above the heads of the astounded guards, Wu Fang waved a mocking hand.

"Thank you!" his voice came faintly from the upper air, "for your hospitality—stupid fools!"

Almost before the guards had caught their breath again, the autogyro with its dangling human burden had dipped behind a nearby hill and was lost to sight. Then the rope was drawn up into the body of the machine by a special windlass, and the escaped prisoner took his seat in the rear cockpit with a satisfied smile.

Hours later, at a hidden rendezvous in the barren hills, the autogyro came to earth where another and more important member of the Conquerors' gang waited with a large transport plane.

"Your discomforts are now at an end, Wu Fang," said the latter. "I am to fly you immediately to the secret headquarters."

In an incredibly short time, Wu Fang, still in his prison clothes, was set down upon Eviloff's secret island in the Caribbean, and was welcomed effusively by the Crime Master. It was a fateful meeting—the Crime Heads of East and West brought together to plot against civilization.

CHAPTER EIGHT
The Crime Master Attacked

Back at the Naval Hospital where Dan Dunn was recovering from his terrific experience on the wrecked pontoon, a serious argument was in progress. The Secret Operative, sitting up in bed, was anxiously warning the Naval Commander against any rash attempts to seize Eviloff on his own fortified island.

"I tell you, Commander," he said, "Eviloff is not only well fortified, with modern weapons and a large crew of disciplined criminals at his command on that island, but he has also, I am convinced, other and more deadly weapons of his own invention—which, if known to the nations at large, would change modern warfare."

"Now, now, Dan," soothed the officer, "don't get excited. I'm afraid your exposure in the water has upset your nerves and you're imagining things beyond reason. What could possibly harm one of our first-line battleships, with its twelve-inch armor plate and huge guns that could blow a little island like Eviloff's clean out of the sea?"

Dan raised a protesting hand.

"I'm not imagining things, Commander," he answered. "Remember it was one of Eviloff's infernal inventions which destroyed the Federal Bank building at a single blow. I tell you, he is prepared to deal with any battleship or other armament you may send against him. Recall that dreadnaught commander, I beg you. You are risking the lives of a thousand men for no good purpose!"

The Commander rose to leave.

"Sorry, Dan, but I'm afraid it can't be done. That battleship will have to take its chances, and I think we did right in sending it. Your idea of going slowly and spying out Eviloff's inventions before we act would be giving the devil too much rope. As it is, we'll bring him up with a short turn."

With a final salute, the officer left the sick room.

In the meantime the mighty battleship sent to round up the criminal band was rapidly nearing its island objective. The commanding officer had called his Executive to the bridge and was giving him final instructions.

"You understand, Lieutenant," he said tersely, "we cannot approach closer than five miles to the island because of this battleship's deep draft and the shoals which surround the island on every hand. We will anchor as closely as possible, however, and send a landing party of sailors and marines ashore in ten small boats. You will convey my compliments and these orders to the officers in charge, and also instruct the gunnery officer to prepare Number One and Two turrets to cover the landing parties with shellfire if the criminals resist."

The battleship, however, had already been sighted by one of Eviloff's scouting planes and accordingly had reported to his headquarters much earlier in the day. It was due to arrive in sight of the island about three hours after dark, and Eviloff as usual had taken clever precautions to warn him of its near approach. Sensitive microphones had been anchored in the shallow water off shore, and these, connected with listening sets on the island, were able to detect the noise of a ship's motors fifty miles away.

At about nine o'clock that evening, the gangster who was listening in beckoned his master toward him and offered the earphones. Eviloff clapped them on his head Microphones Anchored in Shallow Water and listened with scowling face for a full minute.

"The sound is unmistakable," he growled. "Only a dreadnaught's engines could make such a racket—steaming under forced draft! Ha! They little know the fate they are steaming toward. But I know —ha! ha! I know! And it's about time I took charge personally of settling with them... Skearge!" he shouted. And when that tireless individual appeared, he ordered, "Prepare the dirigible for immediate action! I'm going to take it up myself against that clumsy battleship which those stupid fools have sent against us. Have the airship's ground crew stand by and see that every officer and mechanic is in his place. Tell the chief engineer in the powerhouse to give us every kilowatt of power the dynamos can produce, and to be able to cut in all four banks of batteries fully charged within an hour."

His head spinning with the many orders he had to carry out, Skearge departed on the run. Eviloff, knowing that his disciplined helpers would now take charge of everything until the moment he stepped into the ship, re-entered his private office, and sat down to brood wickedly over the death and destruction he was about to let loose.

Around him the island began to hum with activity. In the powerhouse giant dynamos built up their gleaming revolutions to maximum, pouring captive forces into the banked batteries which covered all four walls of a large room. The ground crew led the dirigible out like a great monster on leading strings, while the engine and navigating crews climbed into the big gondola beneath it to check their engines and instruments.

And, all unsuspecting of their fate, the officers and men of the dreadnaught drove their great steel fort through the night seas. At last, orders were received from the bridge to lay to and anchor; for according to his charts the navigating officer had decided that closer approach to the reef-strewn waters of the island would be dangerous. The ship's great anchors plunged downward to grip the sea bottom with their flukes, and the mighty battle-wagon rested motionless on the water, except for a gentle swaying of its fighting tops.

The executive officer gave swift final instructions to the lieutenants and petty officers in charge of the landing forces.

If only he could have known that just above his head, but hidden by thousands of feet of darkness, the Dirigible of Death hovered ready to loose her terrible lightning bolt —he would have ordered every man and officer on the ship to take to the boats and scatter!

But the dirigible's motors were noiseless, and neither searchlights nor night glasses were trained upward from the battleship to seek a possible enemy in the sky.

Eviloff's glasses, however, had been watching the battleship ever since she had come to anchor. And now, in exact striking position above the doomed dreadnaught, the Crime Master gave his last dramatic signals for the loosing of his incredible bolt. All was in order; and the powerhouse this time was ready to give its full quota of electrical energy.

With a wild cry Eviloff gave the signal—!

Out of the night sky blazed suddenly a jagged tongue of light, which, stabbing downward, enveloped the whole warship in blinding radiance. One clap of sky-shaking thunder sounded—and the floating fortress of a thousand fighting men had disappeared beneath the waves.

Only a few moments before, there had been tense excitement in the radio room of the Florida Naval Station, as last-minute reports from the dreadnaught told of its" approach to the Island of Crime.

"We are nearing our destination . . the message came. "The Captain has ordered battle stations ... We have anchored and boats are being lowered for the landing party of marines and sailors... The two gun turrets—"

BANG! BZZZ—BZZZ—

"They've gone dead!" cried the radio operator. "Maybe something's wrong with our end of it— tube burned out or something..."

He twisted the dials rapidly.

"Say! That's funny, sir!" he exclaimed, turning to the radio officer behind him. "I seem to get every other station and wavelength except the battleship's. Trouble's at their end. What shall we do, sir?"

"There's only one thing you can do, Sparks," replied the officer. "Keep tuned in on their wavelength and also on the wave-lengths of the portable emergency sets carried by the lifeboats. Let me know the first thing you get. Probably there's nothing more the matter than a faulty tube in the battleship's sending outfit. We'll give them a half an hour to repair it, and if we hear nothing by that time—"

But a full hour passed without a signal of any kind from the missing battle-wagon. Thoroughly alarmed by this time, the commander of the Naval Station made his way to the sick bay where Dan Dunn, Secret Operative 48, was confined to his bed.

"Sorry I have to disturb you, Dan," he said as he strode into the room, "but I've had a pretty bad shock. I hate to think it, and I won't believe it yet—but I'm beginning to fear that you may have been right in warning us to recall our battleship!"

Dan groaned in dismay.

"I knew it, Commander! I knew something would happen. Quick! Get me my clothes, Commander!, I've got to take a hand myself now, or there'll be more and worse trouble. I'm going to avenge those boys of yours who steamed out to their death a few hours ago!"

"But, Dan—!" protested the Commander. "You're a sick man!"

"I know what I'm talking about, sir," replied Dan. "There's only one explanation of what's happened. Eviloff has turned his lightning machine on the battleship, and that tremendous piece of naval machinery, engines, guns, and all, is right now nothing but a molten blob of metal at the bottom of the ocean. Its crew are ashes floatingon the waves of the Caribbean—

Dan dragged on his shirt.

"Commander!" he grated through clenched teeth. "This mass murder has got to stop! You must risk no more battleships and their crews!"

"But wh-what are you going to do, Dan?" cried the bewildered officer.

"What I am going to do is what should have been done in the first place. I requested you to send out spies to determine Eviloff's strength and to destroy his defenses if possible," retorted Dan with grim emphasis. "You didn't do it, and now a thousand men have gone needlessly to their deaths. From this moment onward I am going to be my own spy! And if I fail—why, there'll be only ONE more man gone. Will you promise to see me on my way, Commander? And then keep hands off until you're convinced that I have failed?"

"Certainly, Dan, I promise," replied the officer instantly. "I'm sure you're throwing your life away with no more chance than our poor boys had. But it's a gallant attempt, and you can count on me for every possible co-operation. After all—who knows? Your chance may be as good as anyone else's."

"Thank you, Commander," replied Dan simply. "Now here's my idea—and keep it absolutely secret, even from your most trusted officers! I'm going to try to get onto the island without being detected —it'll be easier, far easier, for one man than for a big ship's company. If I can, I'll sneak into the interior of the island and watch my chance to get into their powerhouse or their dirigible with a high-explosive bomb. After that—well, who can read the future? The point is, I'm hoping to cripple Eviloff's fighting power temporarily so that your navy boys will have a chance to mop up after me."

"Dan!" cried the Commander with sober enthusiasm, "it's a great scheme, and I think—I really believe you stand some kind of a chance."

CHAPTER NINE
Agent of Retribution

The two had arrived by this time at the float where a navy seaplane rode at anchor. Pulling a set of flying togs from the rear cockpit, Dan put them on as he issued his last requests to the naval commander.

"Are the grenades and dynamite aboard the plane?" Dan asked, fastening his pilot's helmet.

"Yes, everything is ready," the officer assured him.

"Then I'll be off," said Dan, shaking hands in farewell. "We should reach the place where I'm going to get the little sailboat, by nightfall."

The pilot was already in the plane. The moment Dan stepped aboard they were off. He had explained to the naval officer that he intended to pick up a small sailboat to approach the secret island, for he believed that the Crime Master had delicate instruments to warn him of the approach of motor-driven vessels. It was a shrewd deduction on the part of Secret Operative 48.

The naval officer watched the seaplane become a small speck in the sky, and finally disappear into the blue. He realized only too well that Dan Dunn's mission was one of the utmost peril, and that he stood an excellent chance of never coming back alive.

"He has what it takes," the officer murmured admiringly.

Zooming through the atmosphere, Dan and his pilot followed their course until an island came into view.

"I think that must be the nearest island to the one used by Eviloff," said the pilot.

Dan nodded.

"We'll land here, then."

The plane came to a safe landing under the pilot's skilful guidance.

Dan got out.

"I'll walk up to the town and see if I can get a small boat," he told the pilot. "Wait here for me and when I return we can load on the stuff I'll need for the trip."

"All right, Dan," the pilot acknowledged.

Along the beach Dan found just the boat he was looking for. Quickly he entered into negotiations for its purchase.

"Ah, signor," said the owner, with a slight foreign accent. "Eet ees ver' fine boat—you buy him?"

"It looks as though it will serve my purpose," Dan admitted. "I'll take it!"

"You weel find him ver' strong boat," the owner assured him. Pocketing the purchase price, which Dan handed over, the man then offered assistance in launching the craft. "Here, I help you cast off!" he said.

"Thanks, old fellow," Dan expressed his gratitude.

Dan then sailed the boat back along the line of the shore until he came to the seaplane.

"Gee, Dan," said the pilot, "that was quick work! I see you have your sailboat!"

"Yes," Dan answered. "I found a fellow who wanted to sell what I wanted to buy—and we made the deal quickly. Now if you will just help me with the provisions, and that sub-machine gun, and the three powerful dynamite bombs—"

"Sure thing!"

They worked steadily until the necessary articles and equipment were unloaded from the plane into the boat. The provisions included water and food for several days. The bombs were for blowing up the Crime Master's power station—if Dan succeeded in reaching it.

When all was ready, Dan bade the pilot goodby, and set out toward the sunset—alone. The lonely little sailboat was carrying Dan Dunn, Secret Operative 48, to a desperate adventure: a silent contest of wits with the Crime Master.

As for Dan, he was sure he would succeed.