The colors of the mountain changed and blended. The sky to westward was a glory of a myriad colors. Man and girl, high above the world, sat with the rosy glow of dying sunlight in their faces and watched the colors fade and shift into other colors and patterns even more exquisite. Their hands touched. They looked at each other. They smiled queerly, as people smile who are in love or otherwise not quite sane. They moved inevitably closer....

And then the G.C. phone barked raucously:

"All Watch planes attention! Urgent! Extreme high-level traffic reported seven-ten line bound due east, speed over one thousand. All Watch planes put out all detectors and use extra vigilance. Note: the speed, course, and time of report of this traffic checks with Com-Pub observations of moving objects approaching Earth from Mars. This possibility should be considered before opening fire."

Thorn Hard stiffened all over. He got up and swung down to the stubby little ship with its gossamer-like wings of cellate. He touched the report button.

"Plane 257-A reporting seven-ten line. Thorn Hard flying. On Mount Wendel, on leave. Orders?"

He was throwing on the screens even as he reported. And the vertical detector began to whistle shrilly. His eyes darted to the dial, and he spoke again.

"Added report. Detector shows traffic approaching, bound due east, seven hundred miles an hour, high altitude.... Correction; six-fifty miles. Correction; six hundred." He paused. "Traffic is decelerating rapidly. I think, sir, this is the reported ship."

And then there was a barely audible whining noise high in the air to the west. It grew in volume and changed in pitch. From a whine it became a scream. From a scream it rose to a shriek. Something monstrous and red glittered in the dying sunlight. It was huge. It was of no design ever known on earth. Wings supported it, but they were obscured by the blasts of forward rockets checking its speed.

It was dropping rapidly. Then lifting-rockets spouted flame to keep it from too rapid a descent. It cleared a mountain-peak by a bare two hundred feet, some two miles to the south. It was a hundred-odd feet in length. It was ungainly in shape, monstrous in conformation. Colossal rocket-tubes behind it now barely trickled vaporous discharges. It cleared the mountain-top, went heavily on in a steep glide downward, and vanished behind a mountain-flank. Presently the thin mountain air brought the echoed sound of its landing, of rapid-fire explosions of rocket-tubes, and then silence.

Thorn Hard was snapping swift, staccato sentences into the report-transmitter. Describing the clumsy glittering monster, its motion; its wings; its method of propulsion. It seemed somehow familiar despite its strangeness. He said so.

Then a vivid blue flame licked all about the rim of the world and was gone. Simultaneously the G.C. speaker crashed explosively and went dead. Thorn went on grimly, switching in the spare.

"A very violent electrical discharge went out from it then. A blue light seemed to flash all around the horizon at no great distance and my speaker blew out. I have turned on the spare. I do not know whether my sender is functioning—"

The spare speaker cut in abruptly at that moment:

"It is. Stay where you are and observe. A squadron is coming."

Then the voice broke off, because a new sound was coming from the speaker. It was a voice that was unhuman and queerly horrible and somehow machine-like. Hoots and howls and whistles came from the speaker. Wailing sounds. Ghostly noises, devoid of consonants but broadcast on a wave-length close to the G.C. band and therefore produced by intelligence, though unintelligible. The unhuman hoots and wails and whistles came through for nearly a minute, and stopped.

"Stay on duty!" snapped the G.C. speaker. "That's no language known on earth. Those are Martians!"

Thorn looked up to see Sylva standing by the Watch-plane door. Her face was pale in the growing darkness outside.

"Beginning duty sir," said Thorn steadily, "I report that I have with me Miss Sylva West, my fiancÉe, in violation of regulations. I ask that her family be notified."

He snapped off the lights and went with her. The red rocket-ship had landed in the very next valley. There was a glare there, which wavered and flickered and died away.

"Martians!" said Thorn in fine irony. "We'll see when the Watch planes come! My guess is Com-Pubs, using a searchlight! Nervy!"

The glare vanished. There was only silence, a curiously complete and deadly silence. And Thorn said, suddenly:

"There's no wind!"

There was not. Not a breath of air. The mountains were uncannily quiet. The air was impossibly still, for a mountain-top. Ten minutes went by. Twenty. The detector-whistles shrilled.

"There's the Watch," said Thorn in satisfaction. "Now we'll see!"

And then, abruptly, there was a lurid flash in the sky to northward. Two thousand feet up and a mile away, the unearthly green blaze of a hexynitrate explosion lit the whole earth with unbearable brilliance.

"Stop your ears!" snapped Thorn.

The racking concussion-wave of hexynitrate will break human eardrums at an incredible distance. But no sound came, though the seconds went by.... Then, two miles away, there was a second gigantic flash.... Then a third.... But there was no sound at all. The quiet of the hills remained unbroken, though Thorn knew that such cataclysmic detonations should be audible at twenty miles or more. Then lights flashed on above. Two—three—six of them. They wavered all about, darting here and there.... Then one of the flying searchlights vanished utterly in a fourth terrific flash of green.

"The watch planes are going up!" said Thorn dazedly. "Blowing up! And we can't hear the explosions!"

Behind him the G.C. speaker barked his call. He raced to get its message.

"The Watch planes we sent to join you," said a curt voice he recognized as that of the Commanding General of the United Nations, "have located an invisible barrier by their sonic altimeters. Four of them seem to have rammed it and exploded without destroying it. What have you to report?"

"I've seen the flashes, sir," said Thorn unsteadily, "but they made no noise. And there's no wind, sir. Not a breath since the blue flash I reported."

A pause.

"Your statement bears out their report," said the G.C. speaker harshly. "The barrier seems to be hemispherical. No such barrier is known on Earth. These must be Martians, as the Com-Pubs said. You will wait until morning and try to make peaceful contact with them. This barrier may be merely a precaution on their part. You will try to convince them that we wish to be friendly."

"I don't believe they're Martians, sir—"

Sylva came racing to the door of the plane.

"Thorn! Something's coming! I hear it droning!"

Thorn himself heard a dull droning noise in the air, coming toward him.

"Occupants of the rocket-ship, sir," he said grimly, "seem to be approaching. Orders?"

"Evacuate the ship," snapped the G.C. phone. "Let them examine it. They will understand how we communicate and prepare to receive and exchange messages. If they seem friendly, make contact at once."

Thorn made swift certain movements and dived for the door. He seized Sylva and fled for the darkness below the plane. He was taking a desperate risk of falling down the mountain-slopes. The droning drew near. It passed directly overhead. Then there was a flash and a deafening report. A beam of light appeared aloft. It searched for and found Thorn's plane, now a wreck. Flash after flash and explosion after explosion followed....

They stopped. Their echoes rolled and reverberated among the hills. There was a hollow, tremendous intensification of the echoes aloft as if a dome of some solid substance had reflected back the sound. Slowly the rollings died away. Then a voice boomed through a speaker overhead, and despite his suspicions Thorn felt a queer surprise. It was a human voice, a man's voice, full of a horrible amusement.

"Thorn Hardt! Thorn Hardt! Where are you?" Thorn did not move or reply. "If I haff not killed you, you hear me," the voice chuckled. "Come to see me, Thorn Hardt. Der dome of force iss big, yes, but you can no more get out than your friends can get in. And now I haff destroyed your phones so you can no longer chat with them. Come and see me, Thorn Hardt, so I will not be bored. We will discuss der Com-Pubs. And bring der lady friend. You may play der chaperon!"

The voice laughed. It was not pleasant laughter. And the humming drone in the air rose and dwindled. It moved away from the mountain-top. It lessened and lessened until it was inaudible. Then there was dead silence again.

"By his accent, he's a Baltic Russian," said Thorn very grimly in the darkness. "Which means Com-Pubs, not Martians, though we're the only people who realize it; and they're starting a war! And we, Sylva, must warn our people. How are we going to do it?"

She pressed his hand confidently, but it did not look promising. Thorn Hard was on foot, without a transmitter, armed only with his belt-weapons and with a girl to look after, and moreover imprisoned in a colossal dome of force which hexynitrate had failed to crack....

It was August 20, 2037. There was a triple murder in Paris which was rumored to be the work of a Com-Pub spy, though the murderer's unquestionably Gallic touches made the rumor dubious. Newspaper vendor-units were screaming raucously, "Martians land in Colorado!" and the newspapers themselves printed colored-photos of hastily improvised models in their accounts of the landing of a blood-red rocket-ship in the widest part of the Rockies. The inter-continental tennis matches reached their semi-finals in Havana, Cuba. Thorn Hard had not reported to Watch headquarters in twelve hours. Quadruplets were born in Des Moines, Iowa. Krassin, Commissar of Commissars of the Com-Pubs, made a diplomatic inquiry about the rumors that a Martian space-ship had landed in North America. He asked that Com-Pub scientists be permitted to join in the questioning and examination of the Martian visitors. The most famous European screen actress landed from the morning Trans-Atlantic plane with her hair dyed a light lavender, and beauty-shops throughout the country placed rush orders for dye to take care of the demand for lavender hair which would begin by mid-afternoon. The heavy-weight champion of the United Nations was warned that his title would be forfeited if he further dodged a fight with his most promising contender. And ... Thorn Hard had not reported to Watch headquarters in twelve hours.

He was, as a matter of fact, cautiously parting some bushes to peer past a mountain-flank at the red rocket-ship. Sylva West lay on the ground behind him. Both of them weary to the point of exhaustion. They had started their descent from Mount Wendel at the first gray streak of dawn in the east. They had toiled painfully across the broken country between, to this point of vantage. Now Thorn looked down upon the rocket-ship.

It lay a little askew upon the ground, seeming to be partly buried in the earth. A hundred feet and more in length, it was even more obviously a monstrosity as he looked at it in the bright light of day. But now it was not alone. Beside it a white tower reared upward. Pure white and glistening in the sunshine, a bulging, uneven shaft rose a hundred feet sheer. It looked as solid as marble. Its purpose was unguessable. There was a huge, fan-shaped space where the vegetation about the rocket-ship was colored a vivid red. In air-photos, the rocket-ship would look remarkably like something from another planet. But nearby, Thorn could see a lazy trickle of fuel-fumes from a port-pipe on one side of the monster....

"That tower is nothing but cellate foam, which hardens. And Sylva! See?"

She came cautiously through the brushwood and looked down. She shivered a little. From here they could see beneath the bows of the rocket-ship. And there was a name there, in the Cyrillic alphabet which was the official written language of the Com-Pubs. Here, on United Nations soil, it was insolent. It boasted that the red ship came, not from an alien planet, but from a nation more alien still to all the United Nations stood for. The Com-Pubs—the Union of Communist Republics—were neither communistic nor republics, but they were much more dangerous to the United Nations than any mere Martians would have been.

"We'll have some heavy ships here to investigate, soon," said Thorn grimly. "Then I'll signal!"

He flung back his head. High up and far away, beyond that invisible barrier against which Watch-planes had flung themselves in vain, there were tiny motes in mid-air. These were Watch planes too, hovering outside the obstacle they could not see, but which even hexynitrate bombs could not break through. And very far away indeed there was a swiftly-moving small dark cloud. As Thorn watched, that cloud drew close. As his eyes glowed, it resolved itself into its component specks. Small, two-man patrol-scouts. Larger, ten-man cruisers of the air. Huge, massive dreadnaughts of the blue. A complete combat-squadron of the United Nations Fighting Forces was sweeping to position about the dome of force above the rocket-ship.

The scouts swept forward in a tiny, whirling cloud. They sheered away from something invisible. One of them dropped a smoking object. It emitted a vast cloud of paper, which the wind caught and swept away, and suddenly wrapped about a definite section of an arc. More and more of the tiny smoke-bombs released their masses of cloudlike stuff. In mid-air a dome began to take form, outlined by the trailing streaks of gray. It began to be more definitely traced by interlinings. An aerial lattice spread about a portion of a six-mile hemisphere. The top was fifteen thousand feet above the rocket-ship, twenty-five thousand feet from sea-level, as high as Mount Everest itself.

Tiny motes hovered even there, where the smallest of visible specks was a ten-man cruiser. And one of the biggest of the aircraft came gingerly up to the very inner edge of the lattice-work of fog and hung motionless, holding itself aloft by powerful helicopter screws. Men were working from a trailing stage—scientists examining the barrier even hexynitrate would not break down.

Thorn set to work. He had come toilsomely to the neighborhood of the rocket-ship because he would have to do visual signaling, and there was no time to lose. The dome of force was transparent. The air fleet would be trying to communicate through it with the Martians they believed were in the rocket-ship. Sunlight reflected from a polished canteen would attract attention instantly from a spot near the red monster, while elsewhere it might not be observed for a long time. But, trying every radio wave-band, and every system of visual signaling, and watching and testing for a reply, Thorn's signal ought to be picked up instantly.

He handed his pocket speech-light receptor to Sylva. It is standard equipment for all flying personnel, so they may receive non-broadcast orders from flight leaders. He pointed to a ten-man cruiser from which shone the queer electric-blue glow of a speech-light.

"Listen in on that," he commanded. "I'm going to call them. Tell me when they answer."

He began to flash dots and dashes in that quaintly archaic telegraph alphabet Watch fliers are still required to learn. It was the Watch code call, sent over and over again.

"They're trying to make the Martians understand," said Sylva unsteadily with the speech-light receiver at her ear.

Flash—flash—flash.... Thorn kept on grimly. The canteen top was slightly convex, so the sunlight-beam would spread. Accuracy was not needed, therefore. He covered and uncovered it, and covered and uncovered it....

"They answered!" said Sylva eagerly. "They said 'Thorn Hard report at once!'"

There was a hissing, roaring noise over the hillside, where the red rocket-ship lay. Thorn paid no attention. He began to spell out, in grim satisfaction:

"R-o-c-k-e-t s-h-i-p i-s—"

"Look out!" gasped Sylva. "They say look out, Thorn!"

Then she screamed. As Thorn swung his head around, he saw a dense mass of white vapor rushing over the hillside toward them. He picked Sylva up in his arms and ran madly....

The white vapor tugged at his knees. It was a variation of a vortex-stream. He fought his way savagely toward higher ground. The white vapor reached his waist.... It reached his shoulders.... He slung Sylva upon his shoulder and fought more madly still to get out of the wide white current.... It submerged him in its stinging, bitter flood.... As he felt himself collapsing his last conscious thought was the bitter realization that the bulbous white tower had upheld television lenses at its top, which had watched his approach and inspection of the rocket-ship, and had enabled those in the red monster to accurately direct their spurt of gas.

His next sensation was that of pain in his lungs. Something that smarted intolerably was being forced into his nostrils, and he battled against the agony it produced. And then he heard someone chuckle amusedly and felt the curious furry sensation of electric anesthesia beginning....

When he came to himself again a machine was clicking erratically and there was the soft whine of machinery going somewhere. He opened his eyes and saw red all about him. He stirred, and he was free. Painfully, he sat up and blinked about him with streaming, gas-irritated eyes. He had been lying on a couch. He was in a room perhaps fifteen feet by twenty, of which the floor was slightly off-level. And everything in the room was red. Floor and walls and ceiling, the couch he had lain on and the furniture itself. There was a monstrous bulk of a man sitting comfortably in a chair on the other side of the room, pecking at a device resembling a writing-machine.

Thorn sat still for an instant, gaining strength. Then he flung himself desperately across the room, his fingers curved into talons.

Five feet, ten, with the slant of the floor giving him added impetus.... Then his muscles tightened convulsively. A wave of pure agony went through his body. He dropped and lay writhing on the floor, while the high-frequency currents of an induction-screen had their way with him. He was doubled into a knot by his muscles responding to the electric stimulus instead of his will. Sheer anguish twisted him. And the room filled with a hearty bellow of laughter. The monstrous whiskered man had turned about and was shaking with merriment.

He picked up a pocket-gun from beside him and turned off a switch at his elbow. Thorn's muscles were freed.

"Go back, my friendt," boomed the same voice that had come from a speaker the night before. "Go to der couch. You amuse me and you haff already been useful, but I shall haff no hesitation in killing you. You are Thorn Hardt. My name is Kreynborg. How do you do?"

"Where's my friend?" demanded Thorn savagely. "Where is she?"

"Der lady friendt? There!" The whiskered man pointed negligently with the pocket-gun. "I gafe her a bunk to slumber in."

There was a niche in the wall, which Thorn had not seen. Sylva was there, sleeping the same heavy, dreamless sleep from which Thorn himself had just awakened. He went to her swiftly. She was breathing naturally, though tears from the irritating gas still streaked her face and her skin seemed to be pinkened a little from the same cause.

Thorn swung around. His weapons were gone, of course. The huge man snapped on the induction-screen switch again and put down his weapon. With that screen separating the room into two halves, no living thing could cross it without either such muscular paralysis as Thorn had just experienced, or death. Coils in the floor induced alternating currents in the flesh itself, very like those currents used for supposed medical effects in "medical batteries," and "shockers."

"Be calm!" said Kreynborg, chuckling. "I am pleased to haff company. This is der loneliest spot in der Rockies. It was chosen for that reason. But I shall be here for maybe months, and now I shall not be lonely. We of der Com-Pubs haff scientific resources such as your fools haff nefer dreamed of, but there is no scientific substitute for a pretty woman."

He turned again to the writing device. It clicked half a dozen times more, and he stopped. A strip of paper came out of it. He inserted it into the slot of another mechanism and switched on a standard G.C. phone as the paper began to feed. In seconds the room was filled with unearthly hoots and wails and whistles. They came from the device into which the paper was feeding, and they poured into the G.C. transmitter. They went on for nearly a minute, and ceased. Kreynborg shut off the transmitter.

"My code," he observed comfortably, "gifing der good news to Stalingrad. Everything is going along beautifully. I roused der fair Sylva and kissed her a few times to make her scream into a record, and I interpolated her screamings into der last code transmission. Your wise men think der Martians haff vivisected her. They are concentrating der entire fighting force of der United Nations outside der dome of force. And all for a few kisses!"

Thorn was white with rage. His eyes burned with a terrible fury. His hands shook. Kreynborg chuckled again.

"Oh, she is unharmed—so far. I haff not much time now. Presently der two of you will while away der time. But not now."

He switched on the G.C. receiver and the room filled with a multitude of messages. Thorn sat beside Sylva, watching, watching, watching, while invisible machinery whined softly and Kreynborg listened intently to the crisp, curt official reports that came through on the Fighting Force band. Three combat-squadrons were on the spot now; One, Three and Eight. Four more were coming at fast cruising speed—four hundred miles an hour. One combat-squadron of the whole fleet alone would be left to cope with all other emergencies that might arise.... A television screen lighted up and Thorn could see where the lenses on the bulbous tower showed the air all about filled with fighting-planes, hovering about the dome of force like moths beating their wings against a screen. The strongest fighting-force in the world, helpless against a field of electric energy!

"It is amusing," chuckled Kreynborg, looking at the screen complacently. "Der dome of force is a new infention. It is a heterodyning of one frequency upon another at a predetermined distance. It has all der properties of matter except mass and a limit of strength. There is no limit to its strength! But it cannot be made except in a sphere, so at first it seemed only a defensif weapon. With it, we could defy der United Nations to attack us. But we wished to do more. So I proposed a plan, and I haff der honor of carrying it out. If I fail, Krassin disavows me. But I shall not fail, and I shall end as Commissar for der continent of North America!"

He looked wisely at Thorn, who sat motionless.

"You keep quiet, eh, and wait for me to say something indiscreet? Ferry well, I tell you. We are in a sort of gold-fish globe of electric force. Your air fleet cannot break in. You know that! Also, if they were in they could not break out again. So I wait, fery patiently pretending to be a Martian until all your Fighting Force has gathered around in readiness to fight me. But I shall not fight. I shall simply make a new and larger gold-fish globe, outside of this one. And then I go out and make faces at der Fighting Force of der United Nations imprisoned between der two of them—and then der Com-Pub fleet comes ofer!"

He stood up and put his hand on a door-knob.

"Is it not pretty?" he asked blandly. "In two weeks der air fleet will begin to starfe. In three, there will be cannibalism, unless der Com-Pubs accept der surrender. Imagine...." He laughed. "But do not fear, my friendt! I haff profisions for a year. If you are amusing, I feed you. In any case I exchange food for kisses with der charming Sylva. It will be amusing to change her from a woman who screams as I kiss her, to one who weeps for joy. If I do not haff to kill you, you shall witness it!"

He vanished through a doorway on the farther side of the room. Instantly Thorn was on his feet. The dead slumber in which Sylva was sunk was wholly familiar. Electric anesthesia, used not only for surgery, but to enforce complete rest at any chosen moment. He dragged her from that couch to his own. He saw her stir, and her eyes were instantly wide with terror. But Thorn was tearing the couch to pieces. Cover, pneumatic mattress.... He ripped out a loosely-fitting frame-piece of steel.

"Quick,now," he said in a low tone, "I'm going to short the induction-screen. We'll get across it. Then—out the door!"

She struggled to her feet, terrified, but instantly game. Thorn slid the rod of metal across the stretch of flooring he had previously been unable to cross. The induced currents in the rod amounted to a short-circuit of the field. The rod grew hot and its paint blistered smokily. Thorn leaped across with Sylva in his wake. He pointed to the door, and she fled through it. He seized a chair, crashed it frenziedly into the television screen, and had switched on the G.C. phone when there was a roar of fury from Kreynborg. Instantly there was the spitting sound of a pocket-gun and in the red room the racking crash of a hexynitrate pellet. Nothing can stand the instant crash of hexynitrate. Its concussion-wave is a single pulsation of the air. The cellate diaphragm of the G.C. transmitter tore across from its violence and Thorn cursed bitterly. There was no way, now, of signaling....

A second racking crash as a second pellet flashed its tiny green flame. Kreynborg was using a pocket-gun, one of those small terrible weapons which shoot a projectile barely larger than the graphite of a lead pencil, but loaded with a fraction of a milligram of hexynitrate. Two hundred charges would feed automatically into the bore as the trigger was pressed.

Thorn gazed desperately about for weapons. There was nothing in sight. To gain the outside world he had to pass before the doorway through which the bullets had come.... And suddenly Thorn seized the code-writer and the device which transmitted that code as a series of unearthly noises which the world was taking for Martian speech. He swung the two machines before the door in a temporary barrier. Whatever else Kreynborg might be willing to destroy, he would not shoot into them!

Thorn leaped madly past the door as Kreynborg roared with rage again. He paused only to hurl a chair at the two essential machines, and as they dented and toppled, he fled through the door and away.

Sylva peered anxiously at him from behind a huge boulder. He raced toward her, expecting every second to hear the spitting of Kreynborg's pocket-gun. With the continuous-fire stud down, the little gun would shoot itself empty in forty-five seconds, during which time Kreynborg could play it upon him like a hose that spouted death. But Thorn had done the hundred yards in eleven seconds, years before. He bettered his record now. The first of the little green flashes came when he was no more than ten yards from the boulder which sheltered Sylva. The tiny pellet had missed him by inches. Three more, and he was safe from pursuit.

"But we've got to get away!" he panted. "He can shoot gas here and get us again! He can cover four hundred yards with gas, and more than that with guns."

They fled down a tiny water-course, midget figures in an infinity of earth and sky, scurrying frenziedly from a red slug-like thing that lay askew in a mountain valley. Far away and high above hung the war-planes of the United Nations. Big ones and little ones, hovering in hundreds about the outside of the dome of force they could neither penetrate nor understand.

A quarter of a mile. Half a mile. There was no sign from Kreynborg or the rocket-ship. Thorn panted.

"He can't reach us with gas, now, and it looks like he doesn't dare use a gun. They'd know he wasn't a Martian. At night he'll use that helicopter, though. If we can only make those ships see us...."

They toiled on. The sun was already slanting down toward the western sky. At four—by the sun—Thorn could point to a huge air-dreadnaught hanging by lazily revolving gyros barely two miles away. He waved wildly, frantically, but the big ship drifted on, unseeing. The Fighting Force was no longer looking for Thorn and Sylva. They had been carried into the rocket-ship fourteen hours and more before. Sylva's screaming had been broadcast with the weird hoots and whistles the United Nations believed to be the language of inter-planetary invaders. The United Nations believed them dead. Now a watch was being kept on the rocket-ship, to be sure, but it was becoming a matter-of-fact sort of vigilance, pending the arrival of the rest of the Fighting Force and the cracking of the dome of force by the scientists who worked on it night and day.

On level ground, Thorn and Sylva would have reached the edge of the dome in an hour. Here they had to climb up steep hillsides and down precipitous slopes. Four times they halted to make frantic efforts to attract the attention of some nearby ship.

It was six when they came upon the rim. There was no indication of its existence save that three hundred yards from them boughs waved and leaves quivered in a breeze. Inside the dome the air was utterly still.

"There it is!" panted Thorn.

Wearied and worn out as they were, they hurried forward, and abruptly there was something which impeded their movements. They could reach their hands into the impalpable barrier. For one foot, two, or even three. But an intolerable pressure thrust them back. Thorn seized a sapling and ran at the barrier as if with a spear. It went five feet into the invisible resistance and stopped, shot back out as if flung back by a jet of compressed air.

"He told the truth," groaned Thorn. "We can't get out!"

Long shadows were already reaching out from the mountains. Darkness began to creep upward among the valleys. Far, far away a compact dark cloud appeared, a combat-squadron. It swept toward the dome and dissociated into a myriad specks which were aircraft. The fliers already swirling about the invisible dome drew aside to leave a quadrant clear, and Combat-Squadron Seven merged with the rest, making the pattern of dancing specks markedly denser.

"With a fire," said Thorn desperately, "they'll come! Of course! But Kreynborg took my lighter!"

Sylva said hopefully:

"Don't you know some way? Rubbing sticks together?"

"I don't," admitted Thorn grimly, "but I've got to try to invent one. While I'm at it, you watch for fliers."

He searched for dry wood. He rubbed sticks together. They grew warm, but not enough to smoke, much less to catch. He muttered, "A drill, that's the idea. All the friction in one spot." He tugged at the ring under his lapel and the parachute fastened into his uniform collar shot out in a billowing mass of gossamer silk, flung out by the powerful elastics designed to make its opening certain. Savagely, he tore at the shrouds and had a stout cord. He made a drill and revolved it as fast as he could with the cord....

A second dark cloud swept forward in the gathering dusk and merged into the mass of fliers about the dome. Five minutes later, a third. Dense as the air-traffic was, riding-lights were necessary. They began to appear in the deepening twilight. It seemed as if all the sky were alight with fireflies, whirling and swirling and fluttering here and there. But then the fire-drill began to emit a tiny wisp of smoke. Thorn worked furiously. Then a tiny flickering flame appeared, which he nursed with a desperate solicitude. Then a larger flame. Then a roaring blaze! It could not be missed! A fire within the dome could not fail to be noted and examined instantly!

Asearchlight beam fell upon them, illuminating him in a pitiless glare. Thorn waved his arms frantically. He had nothing with which to signal save his body. He flung his arms wide, and up, and wide again, in an improvised adaption of the telegraphic alphabet to gesticulation. He sent the watch call over and over again....

A little cloud of riding-lights swept toward the dome from an infinite distance away. Darkness was falling so swiftly that they were still merely specks of light as they swept up to and seemed to melt into the swirling, swooping mass of fliers about the dome....

Cold sweat was standing out on Thorn's face, despite the violence of his exertions. He was even praying a little.... And suddenly the searchlight beam flickered a welcome answer:

"W-e u-n-d-e-r-s-t-a-n-d. R-e-p-o-r-t."

Thorn flung his arms about madly, sending:

"G-e-t a-w-a-y q-u-i-c-k. C-o-m P-u-b-s h-e-r-e. W-i-l-l m-a-k-e o-t-h-e-r d-o-m-e o-u-t-s-i-d-e t-o t-r-a-p y-o-u."

The searchlight beam upon him flickered an acknowledgment. He knew what was happening after that. The G.C. phones would flash the warning to every ship, and every ship would dash madly for safety.... A sudden, concerted quiver seemed to go over the whirling maze of lights aloft. A swift, simultaneous movement of every ship in flight. Thorn breathed an agonized prayer....

There was a flash of blue light. For one fractional part of a second the stars and skies were blotted out. There was a dome of flame above him and all about the world, of bright blue flame which instantly was—and instantly was not!

Then there was a ghastly blast of green. Hexynitrate going off. In this glare were silhouetted a myriad motes in flight. But there was no noise. A second flare.... And then Thorn Hard, groaning, saw flash after flash after flash of green. Monster explosions. Colossal explosions. Terrific detonations which were utterly soundless, as the ships of the Fighting Force, in flight from the menace of which Thorn had warned them, crashed into an invisible barrier and exploded without cracking it.

It was August 24th, 2037. For three days, now, seven of the eight great combat-squadrons of the United Nations Fighting Forces had been prisoners inside a monstrous transparent dome of force. There was a financial panic of unprecedented proportions in the great financial districts of New York and London and Paris. Martial law was in force in Chicago, in Prague, in Madrid, and in Buenos Aires. The Com-Pubs were preparing an ultimatum to be delivered to the government of the United Nations. Thorn and Sylva were hunted fugitives within the inner dome of force, which protected the red rocket-ship from the seven combat squadrons it had imprisoned. Newspaper vendor-units were shrieking, "Air Fleet Still Trapped!" and a prominent American politician was promising his constituents that if a foreign nation dared invade the sacred territories of the United Nations, a million embattled private planes would take the air. And he seemed not even trying to be humorous! Scientists were wringing their hands in utter helplessness before the incredible resistance of the dome. It had been determined that the dome was a force-field which caused particles charged with positive electricity to attempt to move in a right-hand direction about the source of the field, and particles charged with negative electricity to attempt to move in a left-hand direction. The result was that any effort to thrust an external object into the field of force was an attempt to tear the negatively charged electrons of every atom of that substance, free from the positively charged protons of nuclei. An object could only be passed through the field of force if it ceased to exist as matter—which was not an especially helpful discovery. And—Thorn Hard and Sylva were still hunted fugitives inside the inner dome.

The sun was an hour high when the helicopter appeared to hunt for them by day. After the first time they had never dared light a fire, because Kreynborg in the helicopter searched the hills for a glow of light. But this day he came searching for them by day. Thorn had speared a fish for Sylva with a stick he had sharpened by rubbing it on a crumbling rock. He was working discouragedly on a little contrivance made out of a forked stick and the elastic from his parachute-pack. He was haggard and worn and desperate. Sylva was beginning to look like a hunted wild thing.

Two hundred yards from them the most formidable fighting force the world had ever seen littered the earth with gossamer-seeming cellate wings and streamlined bodies at all angles to each other. And it was completely useless. The least of the weapons of the air-fleet would have been a godsend to Thorn and Sylva. To have had one ship, even the smallest, where they were would have been a godsend to the fleet. But two hundred yards, with the dome of force between, made the fleet just exactly as much protection for Sylva as if it had been a million miles away.

The droning hum of the helicopter came across the broken ground. Now louder, now momentarily muted, its moments of loudness grew steadily more strong. It was coming nearer. Thorn gripped his spear in an instinctive, utterly futile gesture of defense. Sylva touched his hand.

"We'd better hide."

They hid. Thick brush concealed them utterly. The helicopter went slowly overhead, and they saw Kreynborg gazing down at the earth below him. Nearly overhead he paused. And suddenly Thorn groaned under his breath.

"It's the flagship!" he whispered hoarsely to Sylva. "Oh, what fools we were! The flagship! He knows the General would have brought it to earth opposite us, to question us!"

The flagship was nearly opposite. To find the flagship was more or less to find where Thorn and Sylva hid. But they had not realized it until now.

The speaker in the helicopter boomed above their heads.

"Ah, my friends! I think you hear me. Answer me. I haff an offer to make."

Shivering, Sylva pressed close to Thorn.

"Der Com-Pub fleet is on der way," said Kreynborg, chuckling. "Sefen-eights of der United Nations fleet is just outside. You haff observed it. In six hours der Com-Pub fleet begins der conquest of der country and der execution of persons most antagonistic to our regime. But I haff still weary weeks of keeping der air fleet prisoner, until its personnel iss too weak from starfation to offer resistance to our soldiers. So I make der offer. Come and while away der weary hours for me, and I except you both from der executions I shall findt it necessary to decree. Refuse, and I get you anyhow, and you will regret your refusal fery much."

Thorn's teeth ground together. Sylva pressed close to him.

"Don't let him get me, Thorn," she panted hysterically. "Don't let him get me...."

The droning, monotonous hum of the helicopter over their heads continued. The little flying-machine was motionless. The air was still. There was no other sound in the world.

Silence, save for the droning hum of the helicopter. Then something dropped. It went off with an inadequate sort of an explosion and a cloud of misty white vapor reared upward on a hillside and began to settle slowly, spreading out.... The helicopter moved and other things dropped, making a pattern....

"The air's still," said Thorn quite grimly. "That stuff seems to be heavier than air. It's flowing downhill, toward the dome-wall. It will be here in five minutes. We've got to move."

Sylva seemed to be stricken with terror. He helped her to her feet. They began to move toward higher ground. They moved with infinite caution. In the utter silence of this inner dome, even the rustling of a leaf might betray them.

It was the presence of the air fleet within clear view that made the thing so horrible. The defenders of a nation were watching the enemy of a nation, and they were helpless to offer battle. The helicopter hummed and droned, and Kreynborg grinned and searched the earth below him for a sign of the man and girl who had been the only danger to his plan and now were unarmed fugitives. And there were four air-dreadnaughts in plain sight and five thousand men watching, and Kreynborg hunted, for sport, a comrade of the five thousand men and a woman every one of them would have risked or sacrificed his life to protect.

He seemed certain that they were below him. Presently he dropped another gas-bomb, and another. And then Sylva stumbled and caught at something, and there was a crashing sound as a sapling wavered in her grasp.... And Thorn picked her up and fled madly. But billowing white vapor spouted upward before him. He dodged it, and the helicopter was just overhead and more smoke spouted, and more, and more.... They were hemmed in, and Sylva clung close to Thorn and sobbed....

Five thousand men, in a thousand grounded aircraft, shouted curses that made no sound. They waved weapons that were utterly futile. They were as impotent as so many ghosts. Their voices made not even the half-heard whisper one may attribute to a phantom.

The fog-vapor closed over Thorn and Sylva as Kreynborg grinned mockingly at the raging men without the dome of force. He swept the helicopter to a position above the last view of Thorn and Sylva, and the downward-beating screws swept away the foggy gas. Thorn and Sylva lay motionless, though Thorn had instinctively placed himself in a position of defense above her.

The Fighting Force of the United Nations watched, raging, while Kreynborg descended deliberately into the area the helicopter-screws kept clear. While he searched Thorn's pockets reflectively and found nothing more deadly than small pebbles which might strike sparks, and a small forked stick. While he grinned mockingly at the raging armed men and made triumphant gesticulations before carrying Sylva's limp figure to the helicopter. While the little ship rose and swept away toward the rocket-plane.

It descended and was lost to view. Thorn lay motionless on the earth. Seven-eighths of the fighting force of the United Nations was imprisoned within the space between two domes of force no matter could penetrate. A ring two miles across and ten miles in outer diameter held the whole fleet of the United Nations paralyzed.

There was sheer panic through the Americas and Europe and the few outlying possessions of the United Nations.... And it was at this time, with a great fleet already half-way across the Pacific, that the Com-Pubs declared war in a fine gesture of ironic politeness. It was within half an hour of this time that the Seventh Combat Squadron—the only one left unimprisoned—dived down from fifty thousand feet into the middle of the Com-Pub fleet and went out of existence in twenty minutes of such carnage as is still stuff for epics.

The Seventh Squadron died, but with it died not less than three times as many of the foe. And then the Com-Pub fleet came on. Most of the original force remained; surely enough to devastate an undefended nation, to shatter its cities and butcher its people; to slaughter its men and enslave its women and leave a shambles and smoking ash-heaps where the very backbone of resistance to the red flag had been.

It was twenty minutes before Thorn Hard stirred. His lungs seemed on fire. His limbs seemed lead. His head reeled and rocked. He staggered to his feet and stood there swaying dully. A vivid light, brighter than the sunshine, played upon him from the flagship of the fleet which now was helpless to defend its nation. Thorn's befogged brain stirred dazedly as the message came.

"Com-Pub fleet on way. Seventh Combat-Squadron wiped out. Nation defenseless. You are only hope. For God's sake try something. Anything."

Thorn roused himself by a terrific effort. He managed to ask a question by exhausted gestures in the Watch visual alphabet.

"Kreynborg took her to rocket-ship," came the answer. "She recovered consciousness before being carried inside."

And Thorn, reeling on his feet and unarmed and alone, turned and went staggering up a hillside toward the rocket-ship's position. He could only expect to be killed. He could not even hope for anything more than to ensure that Sylva, also, die mercifully. Behind him he left an unarmed nation awaiting devastation, with a mighty air fleet speeding toward it at six hundred miles an hour.

As he went, though, some strength came to him. The fury of his toil forced him to breathe deeply, cleansing his lungs of the stupefying gas which, because it was visible as a vapor, had been carried in the rocket-ship. A visible gas was, of course, more consistent with the early pretense that the rocket-ship bore invaders from another planet. And Thorn became drenched with sweat, which aided in the excretion of the poisonous stuff. His brain cleared, and he recognized despair and discounted it and began to plan grimly to make the most of an infinitesimal chance. The chance was simply that Kreynborg had ransacked his pockets and ignored a little forked stick.

Scrambling up a steep hillside with his face hardened into granite, Thorn drew that from his pocket again. Crossing a hill-top, he stripped off his coat.

He traveled at the highest speed he could maintain, though it seemed painfully deliberate. An hour after he had started, he was picking up small round pebbles wherever he saw them in his path. By the time the tall, bulbous tower was in sight he had picked up probably sixty such pebbles, but no more than ten of them remained in his pockets. They, though, were smooth and round and even, perhaps an inch in diameter, and all very nearly the same size. And he carried a club in his hand.

He went down the last slope openly. The television lenses on the tower would have picked him out in any case, if Kreynborg had repaired the screen. He went boldly up to the rocket-ship.

"Kreynborg!" he called. "Kreynborg!"

He felt himself being surveyed. A door came open. Kreynborg stood chuckling at him with a pocket-gun in his hand.

"Ha! Just in time, my friend! I haff been fery busy. Der Com-Pub fleet is just due to pass in refiew abofe der welcoming United Nations combat-squadrons. I haff been gifing them last-minute information and assurance that der domes of force are solid and can hold forefer. I haff a few minutes to spare, which I had intended to defote to der fair Sylva. But—what do you wish?"

"I'm offering you a bribe," said Thorn, his face a mask. "A billion dollars and immunity to cut off the outer dome of force."

Kreynborg grinned at him.

"It is too late. Besides being a traitor, I would be assassinated instantly. Also, I shall be Commissar for North America anyhow."

"Two billion," said Thorn without expression.

"No," said Kreynborg amusedly. "Throw away der club. I shall amuse myself with you, Thorn Hardt. You shall watch der progress of romance between me and Sylva. Throw away der club!"

The pocket-gun came up. Thorn threw away the club.

"What do you want, if two billion's not enough?"

"Amusement," said Kreynborg jovially. "I shall be bored in this inner dome, waiting for der air fleet to starfe. I wish amusement. And I shall get it. Come inside!"

He backed away from the door, his gun trained on Thorn. And Thorn saw that the continuous-fire stud was down. He walked composedly into the red room in which he had once awakened. Sylva gave a little choked cry at sight of him. She was standing, desperately defiant, on the other side of the induction-screen area on the floor. There was a scorched place on the floor where Thorn had shorted that screen and the bar of metal had grown red-hot. Kreynborg threw the switch and motioned Thorn to her.

"I do not bother to search you for weapons," he said dryly. "I did it so short a time ago. And you had only a club...."

Thorn walked stiffly beside Sylva. She put out a shaking hand and touched him. Kreynborg threw the switch back again.

"Der screen is on," he chuckled. "Console each other, children. I am glad you came, Thorn Hardt. We watch der grand refiew of der Com-Pub fleet. Then I turn a little infention of mine upon you. It is a heat-ray of fery limited range. It will be my method of wooing der fair Sylva. When she sees you in torment, she kisses me sweetly for der prifilege of stopping der heat-ray. I count upon you, my friend, to plead with her to grant me der most extrafagant of concessions, when der heat-ray is searing der flesh from your bones. I feel that she is soft-hearted enough to oblige you. Yes?"

He touched a button and the repaired television-screen lighted up. All the dome of mountains and sky was visible in it. There were dancing motes in sight, which were aircraft.

"I haff remofed all metal-work from that side of der room," added Kreynborg comfortably, "so I can dare to turn my back. You cannot short der induction-screen again. That was clefer. But you face a scientist, Thorn Hardt. You haff lost."

A sudden surge of flying craft appeared on the television screen. The grounded fleet of the United Nations was taking to the air again. In the narrow, two-mile strip between the two domes of force it swirled up and up.... Kreynborg frowned.

"Now, what is der idea of that?" he demanded. He moved closer to the screen. The pocket-gun was left behind, five feet from his finger-tips. "Thorn Hardt, you will explain it!"

"They hope," said Thorn grimly, "your fleet can make gaps in the dome to shoot through. If so, they'll go out through those gaps and fight."

"Foolish!" said Kreynborg blandly. "Der only weapon we haff to use is der normal metabolism of der human system. Hunger!"

Thorn reached into his pocket. Kreynborg was regarding the screen absorbedly. Through the haze of flying dots which was the United Nations fleet, a darkening spot to westward became visible. It drew nearer and grew larger. It was dense. It was huge. It was deadly. It was the Com-Pub battle-fleet, nearly equal to the imprisoned ships in number. It swept up to view its helpless enemy. It came close, so every man could see their only possible antagonists rendered impotent.

Such a maneuver was really necessary, when you think of it. The Com-Pub fleet had encountered one combat-squadron of the United Nations fleet, and that one squadron, dying, had carried down three times its number of enemies. It was necessary to show the Com-Pub personnel the rest of their enemies imprisoned, in order to hearten them for the butchery of civilians before them.

Kreynborg guffawed as the Com-Pub fleet made its mocking circuit of the invisible dome. And Thorn raised his head.

"Kreynborg!" he said grimly. "Look!"

There was something in his tone which made Kreynborg turn. And Thorn held a little forked stick in his hand.

"Turn off the induction-screen, or I kill you!"

Kreynborg looked at him and chuckled.

"It is bluff, my friend," he said dryly. "I haff seen many weapons. I am a scientist! You play der game of poker. You try a bluff! But I answer you with der heat-ray!"

He moved his great bulk, and Thorn released his left hand. There was a sudden crack on Kreynborg's side of the room. A pebble a little over an inch in diameter fell to the floor. Kreynborg wavered, and toppled and fell. Three times more, his face merciless, Thorn drew back his arm, and three times Kreynborg's head jerked slightly. Then Thorn faced the panel on which the induction-screen switch was placed. Several times he thrust his hand through the screen and abruptly drew it back with pain, in an attempt to throw the switch. At last he was successful, and now he walked calmly across the room and bent over the motionless Kreynborg.

"Skull fractured," he said grimly. "All right, Sylva."

He went through the narrow doorway beyond, picking up the pocket-gun as he went. There was a noise of whining machinery. Now Thorn was emptying pellets into the mechanism that controlled the dome of force. There was a crashing of glass. It stopped. There were blows and thumpings. That noise stopped too.

Thorn came back, his eyes glowing. He flung open the outer door of the rocket-ship, and Sylva went to him.

He pointed.

Far away, the Fighting Force of the United Nations was swirling upward. Like smoke from a campfire or winged ants from a tree-stump, they went up in a colossal, twisting spiral. Beyond the domes and above them. The domes existed no longer. Up and up, and up.... And then they swooped down upon the suddenly fleeing enemy. Vengefully, savagely, with all the fury of men avenging not only what they have suffered, but also what they have feared, the combat-squadrons of the United Nations fell upon the invaders. Green hexynitrate explosions lighted up the sky. Ear-cracking detonations reverberated among the mountains. There was battle there, and death and carnage and utter destruction. The roar of combat filled the universe.

Thorn closed the door and looked down at Kreynborg, who breathed stentorously, his mouth foolishly open.

"Our men will be back for us," he said shortly. "We needn't worry." Then he said, "Huh! He called himself a scientist, and he didn't know a sling-shot when he saw one!"

But then Thorn Hard dropped a weapon made of a forked stick and strong elastic from his chute-pack, and caught Sylva hungrily in his arms.