“On the day of the next full moon every living thing on earth will be wiped out of existence--unless you succeed in your mission, Lee.”

Nathaniel Lee looked into the face of Silas Stark, President of the United States of the World, and nodded grimly. “I’ll do my best, Sir,” he answered.

“You have the facts. We know who this self-styled Black Caesar is, who has declared war upon humanity. He is a Dane named Axelson, whose father, condemned to life imprisonment for resisting the new world-order, succeeded in obtaining possession of an interplanetary liner.

“He filled it with the gang of desperate men who had been associated with him in his successful escape from the penitentiary. Together they sailed into Space. They disappeared. It was supposed that they had somehow met their death in the ether, beyond the range of human ken.

“Thirty years passed, and then this son of Axelson, born, according to his own story, of a woman whom the father had persuaded to accompany him into Space, began to radio us. We thought at first it was some practical joker who was cutting in.

[Illustration: _It was like struggling with some vampire creatures in a hideous dream._]

“When our electricians demonstrated beyond doubt that the voice came from outer space, it was supposed that some one in our Moon Colony had acquired a transmitting machine. Then the ships we sent to the Moon Colony for gold failed to return. As you know, for seven weeks there has been no communication with the Moon. And at the last full moon the--blow--fell.

“The world depends upon you, Lee. The invisible rays that destroyed every living thing from China to Australia--one-fifth of the human race--will fall upon the eastern seaboard of America when the moon is full again. That has been the gist of Axelson’s repeated communications.

“We shall look to you to return, either with the arch-enemy of the human race as your prisoner, or with the good news that mankind has been set free from the menace that overhangs it.

“God bless you, my boy!” The President of the United States of the World gripped Nat’s hand and stepped down the ladder that led from the landing-stage of the great interplanetary space-ship.

The immense landing-field reserved for the ships of the Interplanetary Line was situated a thousand feet above the heart of New York City, in Westchester County. It was a flat space set on the top of five great towers, strewn with electrified sand, whose glow had the property of dispersing the sea fogs. There, at rest upon what resembled nothing so much as iron claws, the long gray shape of the vacuum flyer bulked.

Nat sneezed as he watched the operations of his men, for the common cold, or coryza, seemed likely to be the last of the germ diseases that would yield to medical science, and he had caught a bad one in the Capitol, while listening to the debate in the Senate upon the threat to humanity. And it was cold on the landing-stage, in contrast to the perpetual summer of the glass-roofed city below.

But Nat forgot the cold as he watched the preparations for the ship’s departure. Neon and nitrogen gas were being pumped under pressure into the outer shell, where a minute charge of leucon, the newly discovered element that helped to counteract gravitation, combined with them to provide the power that would lift the vessel above the regions of the stratosphere.

In the low roof-buildings that surrounded the stage was a scene of tremendous activity. The selenium discs were flashing signals, and the radio receivers were shouting the late news; on the great power boards dials and light signals stood out in the glow of the amylite tubes. On a rotary stage a thousand feet above the ship a giant searchlight, visible for a thousand miles, moved its shaft of dazzling luminosity across the heavens.

Now the spar-aluminite outer skin of the ship grew bright with the red neon glare. Another ship, from China, dropped slowly to its stage near by, and the unloaders swarmed about the pneumatic tubes to receive the mail. The teleradio was shouting news of a failure of the Manchurian wheat crop. Nat’s chief officer, a short cockney named Brent, came up to him.

“Ready to start, Sir,” he said.

Nat turned to him. “Your orders are clear?”

“Yes, Sir.”

“Send Benson here.”

“I’m here, Sir.” Benson, the ray-gunner in charge of the battery that comprised the vessel’s armament, a lean Yankee from Connecticut, stepped forward.

“You know your orders, Benson? Axelson has seized the Moon and the gold-mines there. He’s planning to obliterate the Earth. We’ve got to go in like mad dogs and shoot to kill. No matter if we kill every living thing there, even our own people who are inmates of the Moon’s penal settlement, we’ve got to account for Axelson.”

“Yes, Sir.”

“We can’t guess how he got those gold-ships that returned with neon and argon for the Moon colonists. But he mustn’t get us. Let the men understand that. That’s all.”

“Very good, Sir.”

The teleradio suddenly began to splutter: A-A-A, it called. And instantly every sound ceased about the landing-stage. For that was the call of Axelson, somewhere upon the Moon.

“Axelson speaking. At the next full moon all the American Province of the World Federation will be annihilated, as the Chinese Province was at the last. There’s no hope for you, good people. Send out your vacuum liners. I can use a few more of them. Within six months your world will be depopulated, unless you flash me the signal of surrender.”

Would the proud old Earth have to come to that? Daily those ominous threats had been repeated, until popular fears had become frenzy. And Nat was being sent out as a last hope. If he failed, there would be nothing but surrender to this man, armed with a super-force that enabled him to lay waste the Earth from the Moon.

Within one hour, those invisible, death-dealing rays had destroyed everything that inhaled oxygen and exhaled carbon. The ray with which the liner was equipped was a mere toy in comparison. It would kill at no more than 500 miles, and its action was quite different.

As a prelude to Earth’s surrender, Axelson demanded that World President Stark and a score of other dignitaries should depart for the Moon as hostages. Every ray fortress in the world was to be dismantled, every treasury was to send its gold to be piled up in a great pyramid on the New York landing-stage. The Earth was to acknowledge Axelson as its supreme master.

The iron claws were turning with a screwlike motion, extending themselves, and slowly raising the interplanetary vessel until she looked like a great metal fish with metal legs ending with suckerlike disks. But already she was floating free as the softly purring engines held her in equipoise. Nat climbed the short ladder that led to her deck. Brent came up to him again.

“That teleradio message from Axelson--” he began.

“Yes?” Nat snapped out.

“I don’t believe it came from the Moon at all.”

“You don’t? You think it’s somebody playing a hoax on Earth? You think that wiping out of China was just an Earth-joke?”

“No, Sir.” Brent stood steady under his superior’s sarcasm. “But I was chief teleradio operator at Greenwich before being promoted to the Province of America. And what they don’t know at Greenwich they don’t know anywhere.”

Brent spoke with that self-assurance of the born cockney that even the centuries had failed to remove, though they had removed the cockney accent.

“Well, Brent?”

“I was with the chief electrician in the receiving station when Axelson was radioing last week. And I noticed that the waves of sound were under a slight Doppler effect. With the immense magnification necessary for transmitting from the Moon, such deflection might be construed as a mere fan-like extension. But there was ten times the magnification one would expect from the Moon; and I calculated that those sound-waves were shifted somewhere.”

“Then what’s your theory, Brent?”

“Those sounds come from another planet. Somewhere on the Moon there’s an intercepting and re-transmitting plant. Axelson is deflecting his rays to give the impression that he’s on the Moon, and to lure our ships there.”

“What do you advise?” asked Nat.

“I don’t know, Sir.”

“Neither do I. Set your course Moonward, and tell Mr. Benson to keep his eyes peeled.”

The Moon Colony, discovered in 1976, when Kramer, of Baltimore, first proved the practicability of mixing neon with the inert new gas, leucon, and so conquering gravitation, had proved to be just what it had been suspected of being--a desiccated, airless desolation. Nevertheless, within the depths of the craters a certain amount of the Moon’s ancient atmosphere still lingered, sufficient to sustain life for the queer troglodytes, with enormous lung-boxes, who survived there, browsing like beasts upon the stunted, aloe-like vegetation.

Half man, half ape, and very much unlike either, these vestiges of a species on a ruined globe had proved tractable and amenable to discipline. They had become the laborers of the convict settlement that had sprung up on the Moon.

Thither all those who had opposed the establishment of the World Federation, together with all persons convicted for the fourth time of a felony, had been transported, to superintend the efforts of these dumb, unhuman Moon dwellers. For it had been discovered that the Moon craters were extraordinarily rich in gold, and gold was still the medium of exchange on Earth.

To supplement the vestigial atmosphere, huge stations had been set up, which extracted the oxygen from the subterranean waters five miles below the Moon’s crust, and recombined it with the nitrogen with which the surface layer was impregnated, thus creating an atmosphere which was pumped to the workers.

Then a curious discovery had been made. It was impossible for human beings to exist without the addition of those elements existing in the air in minute quantities--neon, krypton, and argon. And the ships that brought the gold bars back from the Moon had conveyed these gaseous elements there.

The droning of the sixteen atomic motors grew louder, and mingled with the hum of gyroscopes. The ladder was drawn up and the port hole sealed. On the enclosed bridge Nat threw the switch of durobronze that released the non-conducting shutter which gave play to the sixteen great magnets. Swiftly the great ship shot forward into the air. The droning of the motors became a shrill whine, and then, growing too shrill for human ears to follow it, gave place to silence.

Nat set the speed lever to five hundred miles an hour, the utmost that had been found possible in passing through the earth’s atmosphere, owing to the resistance, which tended to heat the vessel and damage the delicate atomic engines. As soon as the ether was reached, the speed would be increased to ten or twelve thousand. That meant a twenty-two hour run to the Moon Colony--about the time usually taken.

He pressed a lever, which set bells ringing in all parts of the ship. By means of a complicated mechanism, the air was exhausted from each compartment in turn, and then replaced, and as the bells rang, the men at work trooped out of these compartments consecutively. This had been originated for the purpose of destroying any life dangerous to man that might unwittingly have been imported from the Moon, but on one occasion it had resulted in the discovery of a stowaway.

Then Nat descended the bridge to the upper deck. Here, on a platform, were the two batteries of three ray-guns apiece, mounted on swivels, and firing in any direction on the port and starboard sides respectively. The guns were enclosed in a thin sheath of osmium, through which the lethal rays penetrated unchanged; about them, thick shields of lead protected the gunners.

He talked with Benson for a while. “Don’t let Axelson get the jump on you,” he said. “Be on the alert every moment.” The gunners, keen-looking men, graduates from the Annapolis gunnery school, grinned and nodded. They were proud of their trade and its traditions; Nat felt that the vessel was safe in their hands.

The chief mate appeared at the head of the companion, accompanied by a girl. “Stowaway, Sir,” he reported laconically. “She tumbled out of the repair shop annex when we let out the air!”

Nat stared at her in consternation, and the girl stared back at him. She was a very pretty girl, hardly more than twenty-two or three, attired in a businesslike costume consisting of a leather jacket, knickers, and the black spiral puttees that had come into style in the past decade. She came forward unabashed.

“Well, who are you?” snapped Nat.

“Madge Dawes, of the Universal News Syndicate,” she answered, laughing.

“The devil!” muttered Nat. “You people think you run the World Federation since you got President Stark elected.”

“We certainly do,” replied the girl, still laughing.

“Well, you don’t run this ship,” said Nat. “How would you like a long parachute drop back to Earth?”

“Don’t be foolish, my dear man,” said Madge. “Don’t you know you’ll get wrinkles if you scowl like that? Smile! Ah, that’s better. Now, honestly, Cap we just had to get the jump on everybody else in interviewing Axelson. It means such a lot to me.”

Pouts succeeded smiles. “You’re not going to be cross about it, are you?” she pleaded.

“Do you realize the risk you’re running, young woman?” Nat demanded. “Are you aware that our chances of ever getting back to Earth are smaller than you ought to have dreamed of taking?”

“Oh, that’s all right,” the girl responded. “And now that we’re friends again, would you mind asking the steward to get me something to eat? I’ve been cooped up in that room downstairs for fifteen hours, and I’m simply starving.”

Nat shrugged his shoulders hopelessly. He turned to the chief mate. “Take Miss Dawes down to the saloon and see that Wang Ling supplies her with a good meal,” he ordered. “And put her in the Admiral’s cabin. That good enough for you?” he asked satirically.

“Oh that’ll be fine,” answered the girl enthusiastically. “And I shall rely on you to keep me posted about everything that’s going on. And a little later I’m going to take X-ray photographs of you and all these men.” She smiled at the grinning gunners. “That’s the new fad, you know, and we’re going to offer prizes for the best developed skeletons in the American Province, and pick a King and Queen of Beauty!”

“A radio, Sir!”

Nat, who had snatched a brief interval of sleep, started up as the man on duty handed him the message. The vessel had been constantly in communication with Earth during her voyage, now nearing completion, but the dreaded A-A-A that prefaced this message told Nat that it came from Axelson.

“Congratulations on your attempt,” the message ran, “I have watched your career with the greatest interest, Lee, through the medium of such scraps of information as I have been able to pick up on the Moon. When you are my guest to-morrow I shall hope to be able to offer you a high post in the new World Government that I am planning to establish. I need good men. Fraternally, the Black Caesar.”

Nat whirled about. Madge Dawes was standing behind him, trying to read the message over his shoulder.

“Spying, eh?” said Nat bitterly.

“My dear man, isn’t that my business?”

“Well, read this, then,” said Nat, handing her the message. “You’re likely to repent this crazy trick of yours before we get much farther.”

And he pointed to the cosmic-ray skiagraph of the Moon on the curved glass dome overhead. They were approaching the satellite rapidly. It filled the whole dome, the craters great black hollows, the mountains standing out clearly. Beneath the dome were the radium apparatus that emitted the rays by which the satellite was photographed cinematographically, and the gyroscope steering apparatus by which the ship’s course was directed.

Suddenly a buzzer sounded a warning. Nat sprang to the tube.

“Gravitational interference X40, gyroscopic aberrancy one minute 29,” he called. “Discharge static electricity from hull. Mr. Benson, stand by.”

“What does that mean?” asked Madge.

“It means I shall be obliged if you’ll abstain from speaking to the man at the controls,” snapped Nat.

“And what’s that?” cried Madge in a shriller voice, pointing upward.

Across the patterned surface of the Moon, shown on the skiagraph, a black, cigar-shaped form was passing. It looked like one of the old-fashioned dirigibles, and the speed with which it moved was evident from the fact that it was perceptibly traversing the Moon’s surface. Perhaps it was travelling at the rate of fifty thousand miles an hour.

Brent, the chief officer, burst up the companion. His face was livid.

“Black ship approaching us from the Moon, Sir,” he stammered. “Benson’s training his guns, but it must be twenty thousands miles away.”

“Yes, even our ray-guns won’t shoot that distance,” answered Nat. “Tell Benson to keep his guns trained as well as he can, and open fire at five hundred.”

Brent disappeared. Madge and Nat were alone on the bridge. Nat was shouting incomprehensible orders down the tube. He stopped and looked up. The shadow of the approaching ship had crossed the Moon’s disk and disappeared.

“Well, young lady, I think your goose is cooked,” said Nat. “If I’m not mistaken, that ship is Axelson’s, and he’s on his way to knock us galley-west. And now oblige me by leaving the bridge.”

“I think he’s a perfectly delightful character, to judge from that message he sent you,” answered Madge, “and--”

Brent appeared again. “Triangulation shows ten thousand miles, Sir,” he informed Nat.

“Take control,” said Nat. “Keep on the gyroscopic course, allowing for aberrancy, and make for the Crater of Pytho. I’ll take command of the guns.” He hurried down the companion, with Madge at his heels.

The gunners stood by the ray-guns, three at each. Benson perched on a revolving stool above the batteries. He was watching a periscopic instrument that connected with the bridge dome by means of a tube, a flat mirror in front of him showing all points of the compass. At one edge the shadow of the black ship was creeping slowly forward.

“Eight thousand miles, Sir,” he told Nat. “One thousand is our extreme range. And it looks as if she’s making for our blind spot overhead.”

Nat stepped to the speaking-tube. “Try to ram her,” he called up to Brent. “We’ll open with all guns, pointing forward.”

“Very good, Sir,” the Cockney called back.

The black shadow was now nearly in the centre of the mirror. It moved upward, vanished. Suddenly the atomic motors began wheezing again. The wheeze became a whine, a drone.

“We’ve dropped to two thousand miles an hour, Sir,” called Brent.

Nat leaped for the companion. As he reached the top he could hear the teleradio apparatus in the wireless room overhead begin to chatter:

“A-A-A. Don’t try to interfere. Am taking you to the Crater of Pytho. Shall renew my offer there. Any resistance will be fatal. Axelson.”

And suddenly the droning of the motors became a whine again, then silence. Nat stared at the instrument-board and uttered a cry.

“What’s the matter?” demanded Madge.

Nat swung upon her. “The matter?” he bawled. “He’s neutralized our engines by some infernal means of his own, and he’s towing us to the Moon!”

The huge sphere of the Moon had long since covered the entire dome. The huge Crater of Pytho now filled it, a black hollow fifty miles across, into which they were gradually settling. And, as they settled, the pale Earth light, white as that of the Moon on Earth, showed the gaunt masses of bare rock, on which nothing grew, and the long stalactites of glassy lava that hung from them.

Then out of the depths beneath emerged the shadowy shape of the landing-stage.

“You are about to land,” chattered the radio. “Don’t try any tricks; they will be useless. Above all, don’t try to use your puny ray. You are helpless.”

The ship was almost stationary. Little figures could be seen swarming upon the landing-stage, ready to adjust the iron claws to clamp the hull. With a gesture of helplessness, Nat left the bridge and went down to the main deck where, in obedience to his orders, the crew had all assembled.

“Men, I’m putting it up to you,” he said. “Axelson, the Black Caesar, advises us not to attempt to use the Ray-guns. I won’t order you to. I’ll leave the decision with you.”

“We tried it fifteen minutes ago, Sir,” answered Benson. “I told Larrigan to fire off the stern starboard gun to see if it was in working order, and it wasn’t!”

At that moment the vessel settled with a slight jar into the clamps. Once more the teleradio began to scream:

“Open the port hold and file out slowly. Resistance is useless. I should turn my ray upon you and obliterate you immediately. Assemble on the landing-stage and wait for me!”

“You’d best obey,” Nat told his men. “We’ve got a passenger to consider.” He glared at Madge as he spoke, and Madge’s smile was a little more tremulous than it had been before.

“This is the most thrilling experience of my life, Captain Lee,” she said. “And I’ll never rest until I’ve got an X-Ray photograph of Mr. Axelson’s skeleton for the Universal News Syndicate.”

One by one, Nat last, the crew filed down the ladder onto the landing-stage, gasping and choking in the rarefied air that lay like a blanket at the bottom of the crater. And the reason for this was only too apparent to Nat as soon as he was on the level stage.

Overhead, at an altitude of about a mile, the black ship hung, and from its bow a stupendous searchlight played to and fro over the bottom of the crater, making it as light as day. And where had been the mining machinery, the great buildings that had housed convicts and Moon people, and the huge edifice that contained the pumping station, there was--nothing.

The devilish ray of Axelson had not merely destroyed them, it had obliterated all traces of them, and the crew of the liner were breathing the remnants of the atmosphere that still lay at the bottom of the Crater of Pytho.

But beside the twin landing-stages, constructed by the World Federation, another building arose, with an open front. And that front was a huge mirror, now scintillating under the searchlight from the black ship.

“That’s it, Sir!” shouted Brent.

“That’s what?” snapped Nat.

“The deflecting mirror I was speaking of. That’s what deflected the ray that wiped out China. The ray didn’t come from the Moon. And that’s the mirror that deflects the teleradio waves, the super-Hertzian rays that carry the sound.”

Nat did not answer. Sick at heart at the failure of his mission, he was watching the swarm of Moon men who were at work upon the landing-stage, turning the steel clamps and regulating the mechanism that controlled the apparatus. Dwarfed, apish creature, with tiny limbs, and chests that stood out like barrels, they bustled about, chattering in shrill voices that seemed like the piping of birds.

It was evident that Axelson, though he had wiped out the Moon convicts and the Moon people in the crater, had reserved a number of the latter for personal use.

The black ship was dropping into its position at the second landing-stage, connected with the first by a short bridge. The starboard hold swung open, and a file of shrouded and hooded forms appeared, masked men, breathing in condensed air from receptacles upon their chests, and staring with goggle eyes at their captives. Each one held in his hand a lethal tube containing the ray, and, as if by command, they took up their stations about their prisoners.

Then, at a signal from their leader, they suddenly doffed their masks.

Nat looked at them in astonishment. He had not known whether these would be Earth denizens or inhabitants of some other planet. But they were Earth men. And they were old.

Men of sixty or seventy, years, with long, gray beards and wrinkled faces, and eyes that stared out from beneath penthouses of shaggy eyebrows. Faces on which were imprinted despair and hopelessness.

Then the first man took off his mask and Nat saw a man of different character.

A man in the prime of life, with a mass of jet black hair and a black beard that swept to his waist, a nose like a hawk’s, and a pair of dark blue eyes that fixed themselves on Nat’s with a look of Luciferian pride.

“Welcome, Nathaniel Lee,” said the man, in deep tones that had a curious accent which Nat could not place. “I ought to know your name, since your teleradios on Earth have been shouting it for three days past as that of the man who is to save Earth from the threat of destruction. And you know me!”

“Axelson--the Black Caesar,” Nat muttered. For the moment he was taken aback. He had anticipated any sort of person except this man, who stood, looked, and spoke like a Viking, this incarnation of pride and strength.

Axelson smiled--and then his eyes lit upon Madge Dawes. And for a moment he stood as if petrified into a block of massive granite.

“What--who is this?” he growled.

“Why, I’m Madge Dawes, of the Universal News Syndicate,” answered the girl, smiling at Axelson in her irrepressible manner. “And I’m sure you’re not nearly such a bold, bad pirate as people think, and you’re going to let us all go free.”

Instantly Axelson seemed to become transformed into a maniac. He turned to the old men and shouted in some incomprehensible language. Nat and Madge, Brent and Benson, and two others who wore the uniforms of officers were seized and dragged across the bridge to the landing-stage where the black ship was moored. The rest of the crew were ordered into a double line.

And then the slaughter began.

Before Nat could even struggle to break away from the gibbering Moon men to whom he and the other prisoners had been consigned, the aged crew of the Black Caesar had begun their work of almost instantaneous destruction.

Streams of red and purple light shot from the ray-pistols that they carried, and before them the crew of the ether-liner simply withered up and vanished. They became mere masses of human débris piled on the landing-stage, and upon these masses, too, the old men turned their implements, until only a few heaps of charred carbon remained on the landing-stage, impalpable as burned paper, and slowly rising in the low atmospheric pressure until they drifted over the crater.

Nat had cried out in horror at the sight, and tried to tear himself free from the grasp of the Moon dwarfs who held him. So had the rest. Never was struggle so futile. Despite their short arms and legs, the Moon dwarfs held them in an unshakable grip, chattering and squealing as they compressed them against their barrel-like chests until the breath was all but crushed out of their bodies.

“Devil!” cried Nat furiously, as Axelson came up to him. “Why don’t you kill us, too?” And he hurled furious taunts and abuse at him, in the hope of goading him into making the same comparatively merciless end of his prisoners.

Axelson looked at him calmly, but made no reply. He looked at Madge again, and his features were convulsed with some emotion that gave him the aspect of a fiend. And then only did Nat realize that it was Madge who was responsible for the Black Caesar’s madness.

Axelson spoke again, and the prisoners were hustled up the ladder and on board the black vessel.

“The Kommandant-Kommissar will see you!” The door of their prison had opened, letting in a shaft of light, and disclosing one of the graybeards, who stood there, pointing at Nat.

“The--who?” Nat demanded.

“The Kommandant-Kommissar, Comrade Axelson,” snarled the graybeard.

Nat knew what that strange jargon meant. He had read books about the political sect known as Socialists who flourished in the Nineteenth and Twentieth Centuries, and, indeed, were even yet not everywhere extinct. And with that a flash of intuition explained the presence of these old men on board.

These were the men who had been imprisoned in their youth, with Axelson’s father, and had escaped and made their way into space, and had been supposed dead long since. Somewhere they must have survived.

And here they were, speaking a jargon of past generations, and ignorant that the world had changed, relics of the past, dead as the dead Moon from which the black ship was winging away through the ether.

“Don’t go, Captain,” pleaded Madge. “Tell him we’ll all go together.”

Nat shook his head. “Maybe I’ll be able to make terms with him,” he answered, and stepped out upon the vessel’s deck.

The graybeard slammed the door and laughed savagely. “You’ll make no terms with the Black Caesar,” he said. “This is the reign of the proletariat. The bourgeois must die! So Lenin decreed!”

But he stopped suddenly and passed his hand over his forehead like a man awakening from a dream.

“Surely the proletariat has already triumphed on earth?” he asked. “A long time has passed, and daily we expect the summons to return and establish the new world-order. What year is this? Is it not 2017? It is so hard to reckon on Eros.”