Burke found her, rooted to the spot. He had a small metal box in his hand. He didn't notice her pallor nor that she trembled.

"I may have something," he said with careful calm. "The case had this in it. There's a black cube in the box. The case seems to have been made to hold and call attention to this cube. I'll take it up to the instrument-room and use a reader on it."

He led the way. Sandy followed, her throat dry. She knew, of course, that he was under almost intolerable emotional strain. He'd brought her along to be with her for a few moments, but he was so tense that he could think of nothing personal to say. Now it was not possible for him to talk of anything at all.

Yet Sandy realized that even under the stress that pressed upon him, he'd asked her to go look for tools in the gravity-machine room because she'd spoken of possible danger in the opening of the case. He'd gotten her away while he opened it.

When they reached the ship-lock he said briefly, "I want to hurry, Sandy. Wait for me in the ship?"

She nodded, and went to the small spacecraft which had brought them all from Earth.

When she saw Pam, inside, she said shakily, "Is—anybody else here?"

"No," said Pam. "Why?"

Sandy sat down and shivered.

"I think," she said through chattering teeth, "I think I'm going to have hysterics. L-listen, Pam! I—I saw something alive! It was like a bird this high and big as a—There aren't any birds like that! There can't be anything alive here but us! But I saw it! And it saw me and ran away!"

Pam stared and asked questions, at first soothing ones. But presently she was saying indignantly, "I do believe it! That's near the place where I smelled fresh air!"

Of course, fresh air in the asteroid, two hundred and seventy million miles from Earth, was as impossible as what Sandy had seen.

Holmes came in presently, depressed and tired. He'd been filling his mind with the contents of black cubes. He knew how cooking was done in the kitchens of the fortress, some eons since. He knew how to prepare for inspection of the asteroid by a high-ranking officer. He was fully conversant with the bugle-calls once used in the fortress in the place of a public-address loud-speaker system. But he'd found no hint of how the fortress received its supplies, nor how the air was freshened, nor how reinforcements of men used to reach the asteroid. He was discouraged and vexed and weary.

"Sandy," said Pam challengingly, "saw a live bird, bigger than a goose, in the gravity-machine room."

Holmes shrugged.

"Keller's fidgeting," he observed, "because he thinks he's seen movements in the vision-plates that show different inside views of this thing. But he isn't sure that he's seen anything move. Maybe we're all going out of our minds."

"Then Joe's closest," said Pam darkly. "He worries about Sandy!"

"And very reasonably," said Holmes tiredly. "Pam, this business of figuring that there's something deadly on the way and nothing to do about it—it's got me down!"

He slumped in a chair. Pam frowned at him. Sandy sat perfectly still, her hands clenched.

Burke came back twenty minutes later. His expression was studiedly calm.

"I've found out where the garrison went," he said matter-of-factly. "I'm afraid we can't get any help from them. Or anybody else."

Sandy looked at him mutely. He was completely self-controlled, and he did not look like a man resolutely refusing to despair, but Sandy knew him. To her it seemed that his eyes had sunk a little in his head.

"Apparently there's nobody left on the world the garrison came from," said Burke in the tone of someone saying perfectly commonplace things, "so they didn't go back there and there's no use in our trying to make a contact with that world. This was an outpost fortress, you know. It was reached from somewhere far away, and carved out and armed to fight an enemy that didn't attack it for itself, but to get at the world or worlds that made it."

He continued with immoderate calm, "I believe the home world of that civilization has two moons in its sky and something off at the horizon that looks like a hill, but isn't."

"But—"

"The garrison left," explained Burke, "because it was abandoned. It was left behind to stand off the Enemy, and the civilization it belonged to moved away. It was left without supplies, without equipment, without hope. It was left behind even without training to face abandonment, because its members had been trained by black cubes and only knew how to do their own highly special jobs by rote. They were just ordinary soldiers, like the Roman detachments left behind when the legions marched south from Hadrian's Wall and sailed for Gaul. So when there was nothing left for them to do but leave their post or starve—because they couldn't follow the civilization that had abandoned them—they left. The cube in the box was a message they set up for their former rulers and fellow-citizens if they ever returned. It's not a pretty message!"

Sandy swallowed.

"Where'd they go? What happened to them?"

"They went to Earth," said Burke tonelessly. "By twos and fives and dozens, in the service ships that came out with meat, and took back passengers. The service ships had been assigned to bring out what meat the hunting-parties could kill. They took back men who were fighters and ready to face mammoths or sabre tooth tigers or anything else. Just the same, they left a transmitter to call them back if the Enemy ever came again. But it didn't come in their lifetimes, and their descendants forgot. But the transmitter remembered. It called to them. And—we were the ones to answer!"

Sandy hesitated a moment.

"But if the garrison went to Earth," she said dubiously, "what became of them? There aren't any traces—"

"We're traces," said Burke. "They were our ancestors of ten or twenty thousand years ago. They couldn't build a civilization. They were fighting men! Could the Romans left behind at Hadrian's Wall keep up the culture of Rome? Of course not! The garrison went to Earth and turned savage, and their children's children's children built up a new civilization. And for here and for now, we're it. We've got to face the Enemy and drive him back."

He stopped, and said in a tone that was almost completely steady and held no hint of despair, "It's going to be quite a job. But it's an emergency. We've got to manage it somehow."

There was also an emergency on Earth, not simplified as in space by having somebody like Burke accept the burden of meeting it. The emergency stemmed from the fact that despite the best efforts of the air arm of the United States, Burke and the others had gotten out to space. They'd reached the asteroid M-387. Naturally. The United States thereupon took credit for this most creditable achievement. Inevitably. And it was instantly and frantically denounced for suspected space-imperialism, space-monopoly, and intended space-exploitation.

But when Keller's painstaking instructions for the building of gravity-field detectors reached Earth, these suspicions seemed less plausible. The United States passed on the instructions. The basic principle was so new that nobody could claim it, but it was so simple that many men felt a wholesome shame that they had not thought of it before. Nobody could question a natural law which was so obvious once it was stated. And the building of the device required next to no time at all.

Within days then, where the asteroid had a single ten-foot instrument, the United States had a ten-foot, a thirty-foot and a sixty-foot gravity-field detector available to qualified researchers. The new instruments gave data such as no astronomer had ever hoped for before. The thirty-foot disk, tuned for short range, pictured every gravitational field in the solar system. A previously unguessed-at Saturnian moon, hidden in the outer ring, turned up. All the asteroids could be located at one instant. The mystery of the inadequate mass of Pluto was solved within hours of turning on the thirty-foot device.

When the sixty-foot instrument went on, scaled to take in half a hundred light-years of space, the solar system was a dot on it. But four dark stars, one with planets, and twenty-odd planetary systems were mapped within a day. On that same day, though, a query went back to Keller. What, said the query, was the meaning of certain crawling, bright-red specks in mathematically exact relationship to each other, which were visibly in motion and much closer to Earth than Alpha Centaurus? Alpha Centaurus had always been considered the closest of all stars to Earth. Under magnification the bright-red sparks wove and interwove their paths as if about a common center of gravity. If such a thing were not impossible, it would be guessed that they were suns so close together as to revolve about one another within hours. Even more preposterously, they moved through space at a rate which was a multiple of the speed of light. Thirty light-speeds, of course, could not be. And the direction of their motion seemed to be directly toward the glowings which represented the solar system containing Earth. All this was plainly absurd. But what was the cause of this erroneous report from the new device?

Keller wrote out very neatly, "The instrument here shows the same phenomenon. Its appearance much farther away triggered the transmitter here to send the first signals to Earth. Data suggests red dots represent artificial gravity-fields strong enough to warp space and produce new spatial constants including higher speed for light, hence possible higher speed for spacecraft carrying artificial gravity generators. Request evaluation this possibility."

Pam coded it and sent it to Earth. And presently, on Earth, astronomers looked at each other helplessly. Because Keller had stated the only possible explanation. Objects like real suns, if so close together, would tear each other to bits and fuse in flaming novas. Moreover, the pattern of motion of the red-spark-producing objects could not have come into being of itself. It was artificial. There was a group of Things in motion toward Earth's solar system. They would arrive within so many days. They were millions of miles apart, but their gravity-fields were so strong that they orbited each other within hours. If they had gravity-fields, they had mass, which could be as artificial as their gravity. And, whirling about each other in the maddest of dances, ten suns passing through the human solar system could leave nothing but debris behind them.

Oddly enough, the ships that made those gravity-fields might be so small as to be beyond the power of a telescope to detect at a few thousand miles. The destruction of all the solar planets and the sun itself might be accomplished by motes. They would not need to use power for destruction. Gravitation is not expended any more than magnetism, when something is attracted by it. The artificial gravity-fields would only need to be built up. They had been. Once created, they could exist forever without need for added power, just as the sun and planets do not expend power for their mutual attraction, and as the Earth parts with no energy to keep its moon a captive.

The newspapers did not publish this news. But, very quietly, every civilized government on Earth got instructions for the making of a gravity-field detector. Most had them built. And then for the first time in human history there was an actual and desperately honest attempt to poll all human knowledge and all human resources for a common human end. For once, no eminent figure assumed the undignified pose involved in standing on one's dignity. For once, the public remained unworried and undisturbed while the heads of states aged visibly.

Naturally some of the people in the secret frantically demanded that the five in the fortress solve the problem all the science of Earth could not even attack. Incredible lists of required information items went out to Burke and Keller and Holmes. Keller read the lists calmly and tried to answer the questions that seemed to make sense. Holmes doggedly spent all his time experiencing cubes in the hope that by sheer accident he might come upon something useful. Pam, scowling, coded and decoded without pause. And Sandy looked anxiously at Burke.

"I'm going to ask you to do something for me," she said. "When we went down to the Lower Levels, I thought I saw something moving. Something alive."

"Nerves," said Burke. "There couldn't be anything alive in this place. Not after so many years without air."

"I know," acknowledged Sandy. "I know it's ridiculous. But Pam's felt creepy, too, as if there were something deadly somewhere in the rooms we've never been in."

Burke moved his head impatiently. "Well?"

"Holmes found some hand-weapons," said Sandy. "They don't work, of course. Will you fix one for Pam and one for me so that they do?" She paused and added, "Of course it doesn't matter whether we're frightened or not, considering. It doesn't even matter whether there is something alive. It doesn't matter if we're killed. But it would be pleasant not to feel defenseless."

Burke shrugged. "I'll fix them."

She put three of the transparent-barreled weapons before him and said, "I'm going up to the instrument-room and help Pam with her coding."

She went out. Burke took the three hand-weapons and looked at them without interest. But in a technician of any sort there is always some response to a technical problem. A trivial thing like a hand-weapon out of order could hold Burke's attention simply because it did not refer to the coming disaster.

He loosened the hand-grip plates and looked at the completely simple devices inside the weapons. There was a tiny battery, of course. In thousands of years its electrolyte had evaporated. Burke replaced it from the water stores of the ship. He did the same to the other two weapons. Then, curious, he stepped out of the ship's air-lock and aimed at the ship-lock wall. He pressed the trigger. There was a snapping sound and a fragment of rock fell. He tried the others. They fired something. It was not a bullet. The barrels of the weapons, on inspection, were not hollow. They were solid. The weapons fired a thrust, a push, an immaterial blow which was concentrated on a tiny spot. They punched, with nothing solid to do the punching.

"Probably punch a hole right through a man," said Burke, reflectively.

He took the three weapons and went toward the instrument-room. On the way, his mind went automatically back to the coming destruction. It was completely arbitrary. The Enemy had no reason to destroy the human race in this solar system. Men, here, had lost all recollection of their origin and assuredly all memory of enmities known before memory began. If any tradition remained of the fortress, even, it would be hidden in tales of a Golden Age before Pandora was, or of an Age of Innocence when all things came without effort. Those stories were changed out of all semblance to their foundations, of course, as ever-more-ignorant and ever-more-unsophisticated generations retold them. Perhaps the Golden Age was a garbled memory of a time when machines performed tasks for men—before the machines wore out and could not be replaced without other machines to make them. Perhaps the slow development of tools, with which men did things that machines formerly did for them, blurred the accounts of times when men did not need to use tools. Even the everywhere-present traditions of a long, long journey in a boat—the flood legends—might be the last trace of grand-sires' yarns about a journey to Earth. It would have been modified by successive generations who could not imagine a journey through emptiness, and therefore devised a flood as a more scientific and reasonable explanation for myths plainly overlaid with fantasy and superstition.

Burke went into the instrument-room as Sandy was asking, "But how did they? We haven't found any ship-lock except the one we came in by! And if a ship can't travel faster than light without wrapping artificial mass about itself ..."

Holmes had taken off his helmet He said doggedly, "There's nothing about ships in the cubes. Anyhow, the nearest other sun is four light-years away. Nobody'd try to carry all the food a whole colony would need from as far away as that! If they'd used ships for supply, there'd have been hydroponic gardens all over the place to ease the load the ships had to carry! There was some other way to get stuff here!"

"Whatever it was, it didn't bring meat from Earth. That was hauled out, fastened to the outside of service-boats."

"Another thing," Holmes said. "There were thousands of people in the garrison, here. How did the air get renewed? Nobody's found any mention of air-purifying apparatus in the cubes. There's been no sign of any! An emergency air-supply, yes. It was let loose when we came into the ship-lock. But there's no regular provision for purifying the air and putting oxygen into it and breaking down the CO₂!"

"Won't anyone believe I smelled fresh air yesterday?" Pam asked plaintively.

No one commented. It could not be believed. Burke handed Sandy one of the weapons. He gave Pam a second.

"They work very much like the ship-drive, which was developed from them. A battery in the handle energizes them so they use the heat they contain to make a lethal punch without a kick-back. They'll get pretty cold after a dozen or so shots."

He sat down and Holmes went on almost angrily, "The garrison had to get food here. It didn't come in ships. They had to purify the air. They've nothing to do it with! How did they manage?"

Keller smiled faintly. He pointed to a control on the wall.

"If that worked, we could ask. It is supposed to be communication with base. It is turned on. Nothing happens."

"Do you know what I'm thinking?" demanded Holmes. "I'm thinking of a matter-transmitter! It's been pointed out before that we'll never reach the stars in spaceships limited to one light-speed. What good would be voyages that lasted ten, twenty, or fifty years each way? But if there could be matter-transmitters—"

Keller said gently, "Transmitters, no. Transposers, yes."

It was a familiar enough distinction. To break down an object into electric charges and reconstitute it at some distant place would be a self-defeating operation. It could have no actual value. To transmit a hundred and fifty pounds of electric energy—the weight of a man converted into current—would require the mightiest of bus-bars for a conductor, and months of time if it was not to burn out from overload. The actual transmission of mass as electric energy would be absurd. But if an object could simply be transposed from one place to another; if it could be translated from place to place; if it could undergo substitution of surroundings.... That would be a different matter! Transposition would be instantaneous. Translation would require no time. Substitution of position—a man who was here this instant would be there the next—would have no temporal aspect. Such a development would make anything possible. A ship might undertake a voyage to last a century. If a matter-transposer were a part of it, it could be supplied with fuel and air and foodstuffs on its voyage. Its crew could be relieved and exchanged whenever it was desired. And when it made a planet-fall a hundred years and more from home, why, home would still be just around the transposer. With matter-transposition an interstellar civilization could arise and thrive, even though limited to the speed of light for its ships. But a culture spread over hundreds of light-years would be unthinkable without something permitting instant communication between its parts.

"All right!" said Holmes doggedly. "Call them transposers! This fortress had to be supplied. We've found no sign that ships were used to supply it. It needed to have its air renewed and refreshed. We've found no sign of anything but emergency stores of air in case some unknown air-supply system failed. What's the matter with looking for a matter-transposer?"

Burke said, "In a way, a telephone system transposes sound-waves from one place to another. Sound-waves aren't carried along wires. They're here, and then suddenly they're there. But there has to be a sending and receiving station at each end. When the fortress here was 'cut off' from home it could be that its supply-system broke down."

"Its air-system didn't," said Holmes. "It hadn't used up its emergency air-supply. We're breathing it!"

"Anyhow we could try to find even a broken-down transposer," said Sandy.

"You try," said Burke. "Keller's been looking for something for me in the cubes. I'll stay here and help him look."

Sandy examined the weapon he'd given her.

"Pam says she's smelled fresh air, down below where there can't be any. Mr. Keller thought he saw movements in the inside vision-plates, where there can't be any. I still believe I saw something alive in the gravity-machine room, where such a thing is impossible. We're going to look, Pam and I."

Holmes lumbered to his feet.

"I'll come, too. And I'll guarantee to defend you against anything that has survived the ten thousand years or so that this place was without air. My head's tired, after all those cubes."

He led the way. Burke watched as the two girls followed him and closed the door behind them.

"What have you found, Keller?"

"A cube about globes," said Keller. "Very interesting."

"Nothing on communication with base?"

Keller shook his head.

Burke said evenly, "I figured out three chances for us—all slim ones. The first was to find the garrison when the radio summons didn't and get it or its descendants to help. I found the garrison—on Earth. No help there. The second chance was finding the civilization that had built this fortress. It looks like it's collapsed. There's been time for a new civilization to get started, but it's run away. The third chance is the slimmest of all. It's hooking together something to fight with."

Keller reached out over the array of cubes that had been experienced by Holmes and himself while using the helmets from the cube-library. One cube had been set aside. Keller put it in place on the extra helmet and handed it to Burke.

"Try it," said Keller.

Burke put the helmet on his head.

He was in this same instrument-room, but he wore a uniform and he sat at an instrument-board. He knew that there were drone service-boats perhaps ten thousand miles out, perhaps a hundred. They'd been fitted out to make a mock attack on the fortress. Counter-tactics men devised them. There was reason for worry. Three times, now, drones pretending to be Enemy ships had dodged past the screen of globes set out to prevent just such an evasion. Once, one of the drones had gloatingly touched the stone of the fortress' outer surface. This was triumph for the counter-tactics crew, but it was proof that an Enemy ship could have wiped out the fortress and all its garrison a hundred times over.

Burke sweated. There was a speck with a yellow ring about it. It was a globe, poised and ready to dart in any conceivable direction if an Enemy detection-device ranged it. The globes did not go seeking an Enemy. They placed themselves where they would be sought. They set themselves up as targets. But when a radar-pulse touched them, they flung themselves at its source, their reflex chooser-circuits pouring incredible power into a beam of the same characteristics as the radar-touch. That beam, of course, paralyzed or burned out the Enemy device necessarily tuned to it. And the globes plunged at the thing which had found them. They accelerated at a hundred and sixty gravities and mere high explosive would be wasted if they carried it. Nothing could stand their impact. Nothing!

But in drills three drones had dodged them. The counter-tactics men understood the drones, of course, as it was hoped the Enemy did not. But it should not be possible to get to the fortress! If the fortress was vulnerable, so was the Empire. If the Empire was vulnerable, the Enemy would wreck its worlds, blast its cities, exterminate its population and only foulness would remain in the Galaxy.

On the monitor-board a light flashed. A line of green light darted across the screen. It was the path of a globe hurtling toward something that had touched it with a radar-frequency signal. The acceleration of the globe was breathtaking. It seemed to explode toward its target.

But this globe hit nothing. It went on and on.... A second globe sprang. It also struck nothing. It went away to illimitable emptiness. Its path exactly crossed that of the first. A third and fourth and fifth.... Each one flung itself ferociously at the source of some trickle of radiation. Their trails crossed at exactly the same spot. But there was nothing there....

Burke suddenly flung up a row of switches, inactivating the remaining globes under his control. Five had flung themselves away, darting at something which radiated but did not exist. Something which was not solid. Which was not a drone ship impersonating an Enemy. They'd attacked an illusion....

At the control-board. Burke clenched his fist and struck angrily at the flat surface before him. An illusion! Of course!

Cunningly, he made adjustments. He had five globes left. He chose one and changed the setting of its reflex chooser-circuit. It would ignore radar frequencies now. It would pick up only stray radiation—induction frequencies from a drone ship with its drive on.

The globe's light flashed. A train of green fire appeared. A burst of flame. A hit! The drone was destroyed. He swiftly changed the setting of the reflex circuits of the rest. Two! Three! Three drones blasted in twice as many seconds.

He mopped his forehead. This was only a drill, but when the Enemy came it would be the solution of such problems that would determine the survival of the fortress and the destruction of the Enemy.

He reported his success crisply.

Burke took off the helmet.

Keller said mildly, "What did he do?"

Burke considered.

"The drone, faking to be an enemy, had dumped something out into space. Metal powder, perhaps. It made a cloud in emptiness. Then the drone drew off and threw a radar-beam on the cloud of metal particles. The beam bounced in all directions. When a globe picked it up, it shot for the phony metal-powder target. It went right through and off into space. Other globes fell for the same trick. When they were all gone, the drones could have come right up to the fort."

He was almost interested. He'd felt, at least, the sweating earnestness of an unknown member of this garrison, dead some thousands of years, as he tried to make a good showing in a battle drill.

"So he changed the reflex circuits," Burke added. "He stopped his globes from homing on radar frequencies. He made them home on frequencies that wouldn't bounce." Then he said in surprise, "But they didn't hit, at that! The drones blew up before the globes got to them! They were exploding from the burning-out of all their equipment before the globes got there!"

Keller nodded. He said sorrowfully, "So clever, our ancestors. But not clever enough!"

"Of our chances," said Burke, "or what I think are chances, the least promising seems to be the idea of trying to hook something together to fight with." He considered, and then smiled very faintly. "You saw movements you couldn't identify in the vision-plates? Sandy says she saw something alive. I wonder if something besides us answered the space-call and got into the fortress by a different way, and has been hiding out, afraid of us."

Keller shook his head.

"I don't believe it either," admitted Burke. "It seems crazy. But it might be true. It might. I'm scraping the bottom of the barrel for solutions to our problem."

Keller shook his head again. Burke shrugged and went out of the instrument-room. He went down the stairs and the first long corridor, and past the long rows of emplacements in which were set the hunkering metal monsters he'd cube-dreamed of using, but which would be of no conceivable use against speeding, whirling, artificial-gravity fields with the pull and the mass of suns.

He reached the last long gallery on which the ship-lock opened. He saw the broad white ribbon of many strands of light, reaching away seemingly without limit. And he saw a tiny figure running toward him. It was Sandy. She staggered as she ran. She had already run past endurance, but she kept desperately on. Burke broke into a run himself.

When he met her, she gasped, "Pam! She—vanished—down below! We were—looking, and Pam cried out. We ran to her. Gone! And we—heard noises! Noises! Holmes is searching now. She—screamed, Joe!"

Burke swung her behind him.

"Tell Keller," he commanded harshly. "You've got that hand-weapon? Hold on to it! Bring Keller! We'll all search! Hurry!"

He broke into a dead run.

It might have seemed ironic that he should rush to help Sandy's sister in whatever disaster had befallen her when they were facing the end of the whole solar system. In cold blood, it couldn't be considered to matter. But Burke ran.

He panted when he plunged down the ramp to the lower portions of the asteroid. He reached the huge cavern in which the motionless power-generator towered storeys high toward a light-laced ceiling.

"Holmes!" he shouted, and ran on. "Holmes!"

He'd been no farther than this, before, but he went on into tunnels with only double lines of light-tubes overhead, and he shouted and heard his own voice reverberating in a manner which seemed pure mockery. But as he ran he continued to shout.

And presently Holmes shouted in return. There was a process of untangling innumerable echoes, and ultimately they met. Holmes was deathly white. He carried something unbelievable in his hands.

"Here!" he growled. "I found this. I cornered it. I killed it! What is it? Did things like this catch Pam?"

Only a man beside himself could have asked such a question. Holmes carried the corpse of a bird with mottled curly feathers. He'd wrung its neck. He suddenly flung it aside.

"Where's Pam?" he demanded fiercely. "What the hell's happened to her? I'll kill anything in creation that's tried to hurt her!"

Burke snapped questions. Inane ones. Where had Pam been last? Where were Holmes and Sandy when they missed her? When she cried out?

Holmes tried to show him. But this part of the asteroid was a maze of corridors with uncountable doorways opening into innumerable compartments. Some of these compartments were not wholly empty, but neither Burke nor Holmes bothered to examine machine-parts or stacks of cases that would crumble to dust at a touch. They searched like crazy men, calling to Pam.

Keller and Sandy arrived. They'd passed the corpse of the bird Holmes had killed, and Keller was strangely white-faced. Sandy panted, "Did you find her? Have you found any sign?"

But she knew the answer. They hadn't found Pam. Holmes was haggard, desperate, filled with a murderous fury against whatever unnameable thing had taken Pam away.

"Here!" snapped Burke. "Let's get some system into this! Here's the case with the message-cube. It's our marker. We start from here! I'll follow this cross corridor and the next one. You three take the next three corridors going parallel. One each! Look in every doorway. When we reach the next cross-corridor we'll compare notes and make another marker."

He went along the way he'd chosen, looking in every door. Cryptic masses of metal in one compartment. A heap of dust in another. Empty. Empty. A pile of metal furniture. Another empty. Still another.

Holmes appeared, his hands clenching and unclenching. Sandy turned up, struggling for self-control.

"Where's Keller?"

"I heard him call out," said Sandy breathlessly. "I thought he'd found something and I hurried—"

He did not come. They shouted. They searched. Keller had disappeared. They found the mark they'd started from and retraced their steps. Burke heard Holmes swear startledly, but there were so many echoes he could not catch words.

Sandy met Burke. Holmes did not. He did not answer shouts. He was gone.

"We stay together," said Burke in an icy voice. "We've both got hand-weapons. Keep yours ready to fire. I've got mine. Whatever out of hell is loose in this place, we'll kill it or it will kill us, and then—"

He did not finish. They stayed close together, with Burke in the lead.

"We'll look in each doorway," he insisted. "Keep that pistol ready. Don't shoot the others if you see them, but shoot anything else!"

"Y-yes," said Sandy. She swallowed.

It was nerve-racking. Burke regarded each doorway as a possible ambush. He investigated each one first, making sure that the compartment inside it was wholly empty. There was one extra-large archway to an extra-large compartment, halfway between their starting point and the next cross-corridor. It was obviously empty, though there was a large metal plate on the floor. But it was lighted. Nothing could lurk in there.

Burke inspected the compartment beyond, and the one beyond that.

He thought he heard Sandy gasp. He whirled, gun ready.

Sandy was gone.