Greg stared at him. "But if it wasn't an ore strike, what was it?"

"I don't know," Johnny said. "But I'm sure of one thing ... it was something important enough that he was ready to die before he'd reveal it. And that means it was important enough that Tawney won't dare kill us until he finds out what it was."

9. The Invisible Man

Crouching back into the shadow, Tom Hunter waited as the heavy footsteps moved up the corridor, then back down, then up and down again. He peered around the corner for a moment, looking quickly up and down the curving corridor. The guard was twenty yards away, moving toward him in a slow measured pace. Tom jerked his head back, then peered out again as the footsteps receded.

The guard was a big man, with a heavy-duty stunner resting in the crook of his elbow. He paused, scratched himself, and resumed his pacing. Tom waited, hoping that something might distract the big man, but he moved stolidly back and forth, not too alert, but far too alert to risk breaking out into the main corridor.

Tom moved back into the darkened corridor where he was standing, trying to decide what to do. It was a side corridor, and a blind alley; it ended in a large hatchway marked HYDROPONICS, and there were no branching corridors. If he were discovered here, there would be no place to hide.

But he knew that he could never hope to accomplish his purpose here....

A hatch clanged open, and there were more footsteps down the main corridor as a change of guards hurried by. There was a rumble of voices, and Tom listened to catch the words.

"... don't care what you think, the boss says tighten it up...."

"But they got them locked in...."

"So tell it to the boss. We're supposed to check every compartment in the section every hour. Now get moving...."

The footsteps moved up and down the corridor then, and Tom heard hatches clanging open. If they sent a light down this spur ... he turned to the hatch, spun the big wheel on the door, and slipped inside just as the footsteps came closer.

The stench inside was almost overpowering. The big, darkened room was extremely warm, the air damp with vapor. The plastic-coated walls streamed with moisture. Against the walls Tom could see the great hydroponic vats that held the yeast and algae cultures that fed the crew of the ship. Water was splashing in one of the vats, and there was a gurgling sound as nutrient broth drained out, to be replaced with fresh.

He moved swiftly across the compartment, into a darkened area behind the rows of vats, and crouched down. He heard footsteps, and the ring of metal as the hatchway came open. One of the guards walked in, peered into the gloom, wrinkled his nose, and walked out again, closing the hatchway behind him.

It would do for a while ... if he didn't suffocate ... but if this ship was organized like smaller ones, it would be a blind alley. Modern hydroponic tanks did not require much servicing, once the cultures were growing; the broth was drained automatically and sluiced through a series of pipes to the rendering plant where the yeasts could be flavored and pressed into surrogate steaks and other items for s.p.a.ceship cuisine. There would be no other entrances, no way to leave except the way he had come in.

And with the guards on duty, that was out of the question. He waited, listening, as the check-down continued in nearby compartments. Then silence fell again. The heavy yeast aroma had grown more and more oppressive; now suddenly a fan went on with a whir, and a cool draft of freshened reprocessed air poured down from the ventilator shaft above his head.

Getting into the orbit-ship had been easier than he had hoped. In the excitement as the new prisoners were brought aboard, security measures had been lax. No one had expected a third visitor; in consequence, no one looked for one. Huge as it was, the Jupiter Equilateral ship had never been planned as a prison, and it had taken time to stake out the guards in a security system that was at all effective. In addition, every man who served as a guard had been taken from duty somewhere else on the ship.

So there had been no guard at the airlock in the first few moments after the prisoners were taken off the Ranger ship. Tom had waited until the ship was moored, clinging to the fin strut. He watched Greg and Johnny taken through the lock, and soon the last of the crew had crossed over after securing the ship. Presently the orbit-ship airlock had gone dark, and only then had he ventured from his place of concealment, creeping along the dark hull of the Ranger ship and leaping across to the airlock.

A momentary risk, then, as he opened the lock. In the control room, he knew, a signal light would blink on a panel as the lock was opened. Tom moved as quickly as he could, hoping that in the excitement of the new visitors, the signal would go unnoticed ... or if spotted, that the spotter would a.s.sume it was only a crewman making a final trip across to the Ranger ship.

But once inside, he began to realize the magnitude of his problem. This was not a tiny independent orbit-ship with a few corridors and compartments. This was a huge ship, a vast complex of corridors and compartments and holds. There was probably a crew of a thousand men on this ship ... and there was no sign where Greg and Johnny might have been taken.

He moved forward, trying to keep to side corridors and darkened areas.

In the airlock he had wrapped up his pressure suit and stored it on a rack; no one would notice it there, and it might be handy later. He had strapped his father's gun case to his side, some comfort, but a small one.

Now, crouching behind the yeast vat, he lifted out the gun, hefted it idly in his hand. It was a weapon, at least. He was not well acquainted with guns, and in the shadowy light it seemed to him that this one looked odd for a revolver; it even felt wrong, out of balance in his hand. He slipped it back in the case. After all, it had been fitted to Dad's hand, not his. And Johnny or Greg would know how to use it better than he would.

If he could find them. But to do that, he would have to search the ship.

He would have to move about, he couldn't just wait in a storage hold.

And with all the guards that were posted, he would certainly stumble into one of them sooner or later if he tried leaving this spot....

He shook his head, and started for the hatch. He would have to chance it. There was no way to tell how much time he had, but it was a sure bet that he didn't have very long.

In the spur corridor again, he waited until the guard's footsteps were m.u.f.fled and distant. Then he darted out into the main corridor, moving swiftly and silently away from the guard. At the first hatchway he ducked inside, waited in the darkness, panting....

The guard had stopped walking. Then his footsteps resumed, but more quickly, coming down the corridor. He stopped, almost outside the hatchway door. "Funny," Tom heard him mutter. "I'd have sworn...."

Tom held his breath, waiting. This was a storage hold, but he didn't dare to move, even to take cover. The guard stood motionless for a moment, then grunted, and resumed his slow pacing.

When he had moved away Tom caught his breath in huge gasps, his heart beating in his throat. It was no use, he thought in despair. Once or twice he might get away with it, but sooner or later a guard would be alert enough to investigate an obscure noise, a flicker of movement in the corner of his eye....

There had to be another way. His eye probed the storage hold, hopelessly, and then stopped on a metal grill in the wall.

For a moment, he didn't recognize what it was. Then there was a _whoosh-whoosh-whoosh_ as a fan went on, and he felt cool air against his cheek. He held out his hand to the grill, found the air coming from there.

A ventilation shaft. Every s.p.a.ce craft had to have reconditioning units for the air inside the ship; the men inside needed a constant supply of fresh oxygen, but even more, without pumps to move the air in each compartment they would soon suffocate from the acc.u.mulation of carbon dioxide in the air they breathed out, or bake from the heat their bodies radiated. On the other hand, the yeasts and algae required carbon dioxide and yielded copious amounts of oxygen as they grew.

In Roger Hunter's little orbit-ship the ventilation shafts were small, a loose network of foot-square ducts leading from the central pumps and air-reconditioning units to every compartment in the ship. But in a ship of this size....

The grill was over a yard wide, four feet tall. It started about shoulder height and ran up to the overhead. The ducts would network the ship, opening into every compartment, and no one would ever open them unless something went wrong.

And then he was laughing out loud, working the grill out of the slots that held it to the wall, trying to make his hands work in his excitement.

He knew he had found his answer.

The grill came loose, lifted down in a piece. He stopped short as footsteps approached in the corridor, paused, and went on. Then he peered into the black gaping hole behind the grill. It was big enough for a man to crawl in. He shinned up into the hole, and pulled the grill back into its slot behind him.

Somewhere far away he heard a throbbing of giant pumps. There was a rush of cool fresh air past his cheek, cold when it contacted the sweat pouring down his forehead. He could not quite stand up, but there was plenty of room for him to crouch and move.

Ahead of him was a black tunnel, broken only by a patch of light coming through the grill that opened into the next compartment. He started into the blackness, his heart racing.

Somewhere in the ship Johnny Coombs and Greg Hunter were prisoners ... but now, Tom knew, there was a way to escape.

It was a completely different world, a world within a world, a world of darkness and silence, of a thousand curving and intersecting tunnels, some large, some small. For hours it seemed to him that he had been wandering through a tomb, moving through the corridors of a dead ship, the lone surviving crewman. There was some contact with the other world, of course, the world of the s.p.a.ceship outside ... each compartment had its metal grill, and he pa.s.sed many of them. But there were like doors that only he knew existed. He met no one in _these_ corridors, there was no danger of sudden discovery and arrest in these dark alleys....

His boots had made too much noise as he started out, so he had slipped them off, hanging them from his belt and moving on in his stocking feet.

As he went from duct to duct, he had an almost ridiculous feeling of freedom and power. In every sense, he was an invisible man. Not one soul on this great ship knew he was here, or even suspected. He had the run of the ship, complete freedom to go wherever he chose. He could move from compartment to compartment as silently and invisibly as if he had no substance at all.

He knew the first job was to learn the pattern of the ducts, and orientation was a problem. He had heard stories of men getting lost in the deep underground mining tunnels on Mars, wandering in circles for days until their food gave out and they starved. And there was that hazard here, for every duct looked like every other one.

But there was a difference here, because the ducts curved just as the main ship's corridors did. He could always identify the center of the ship by the force of false gravity pulling the other way. Furthermore, as the ducts drew closer to the pumps and reconditioning units, they opened into larger vents, and the noise of the pumps thundered in his ears. After an hour of exploration, Tom was certain that from any place in the ship he could at least find his way to the outer layer, and from there to one of the scout-ship airlocks.

Finding Greg and Johnny was quite a different matter.