There were many of these structures circling Earth; every nation on the globe maintained at least one, and usually several. Hart had visited one of those belonging to his own country, partly for technical familiarity and partly to accustom himself to weightlessness. He had studied its plans with care, and scientists had carefully explained to him the functions of each part, and the ways in which the launchers of the Western Alliance were likely to differ. Most important, they had described to him several ways by which such structures might be destroyed. Hart's smile was wolfish as he thought of that; these people who preferred the pleasures of personal liberty to those of efficiency would see what efficiency could do.
But this delay was not efficient. He had made his plans long before, and it was more than time to set about their execution. He must be reasonably near a store of rocket fuel; and some at least of the air in this station must contain a breathable percentage of oxygen. Without further deliberation, he opened the door and floated out into the corridor.
He did not go blindly. Tiny detectors built into the wrists of his suit reacted to the infrared radiations, the water vapor and carbon dioxide and even the breathing sounds that would herald the approach of a human being — unless he were wearing a nonmetallic suit similar to Hart's own. Apparently the personnel of the base did not normally wear these, however, for twice in the first ten minutes the saboteur was warned into shelter by the indications of the tiny instruments. In that ten minutes he covered a good deal of the outer zone.
He learned quickly that the area in which a carbon dioxide atmosphere was maintained was quite limited in extent, and probably constituted either a quarantine zone for newly arrived supplies, or a food storage area. It was surrounded by an uninterrupted corridor lined on one side with airtight doors leading into the COs rooms, and on the other by flimsier portals closing off other storage spaces. Hart wondered briefly at the reason for such a vast amount of storage room; then his attention was taken by another matter. He had been about to launch himself in another long, weightless glide down the corridor in search of branch passages which might lead to the rocket fuel stores, when a tiny spot on one wall caught his eye.
He instantly went to examine it more closely, and as quickly recognized a photoelectric eye. There appeared to be no lens, which suggested a beam-interruption unit; but the beam itself was not visible, nor could he find any projector. That meant a rather interesting and vital problem lay in avoiding the ray. He stopped to think.
In the scanning room on the second level, Dr. Bruce Mayhew chuckled aloud.
“It's wonderful what a superiority complex can do. He's stopped for the first time — didn't seem to have any doubts of his safety until he spotted that eye. The old oil about `decadent democracies' seems to have taken deep hold somewhere, at least. He must be a military agent rather than a scientist.”
Warren Floyd nodded. “Let's not pull the same boner, though,” he suggested. “Scientist or not, no stupid man would have been chosen for such a job. Do you think he's carrying explosives? One man could hardly have chemicals enough to make a significant number of breaches in the outer shell.”
“He may be hoping to get into the core, to set off a war head,” replied the older man, “though I don't for the life of me see how he expects to do it. There's a rocket fuel in his neighborhood, of course, but it's just n.v. for the torpedoes — harmless, as far as we're concerned.”
“A fire could be quite embarrassing, even if it weren't an explosion,” pointed out his assistant, “particularly since the whole joint is nearly pure magnesium. I know it's sinfully expensive to transport mass away from Earth, but I wish they had built this place out of something a little less responsive to heat and oxygen.”
“I shouldn't worry about that,” replied Mayhew. “He won't get a fire started.”
Floyd glanced at the flanking screens which showed armored men keeping pace with the agent in parallel corridors, and nodded. “I suppose not — provided Ben and his crew aren't too slow closing in when we give the signal.”
“You mean when I give the signal,” returned the other man. “I have reasons for wanting him free as long as possible. The longer he's free, the lower the opinion he'll have of us; when we do take him, he'll be less ready to commit suicide, and the sudden letdown of his self-confidence will make interrogation easier.”
Floyd privately hoped nothing would happen to deflate his superior's own self-confidence, but wisely said nothing; and both men watched Hart's progress almost silently for some minutes. Floyd occasionally transmitted a word or two to the action party to keep them apprised of their quarry's whereabouts, but no other sound interrupted the vigil.
Hart had finally found a corridor which branched away from the one he had been following, and he proceeded cautiously along it. He had learned the intervals at which the photocells were spotted, and now avoided them almost automatically. It did not occur to him that, while the sight of a spacesuited man in the outer corridors might not surprise an observer, the presence of such a man who failed consistently to break the beams of the photocell spotters would be bound to attract attention. The lenses of the scanners were too small and too well hidden for Hart to find easily, and he actually believed that the photocells were the only traps. With his continued ease in avoiding them, his self-confidence and contempt for the Westerners were mounting as Mayhew had foretold.
Several times he encountered air breaks — sliding bulkheads actuated by automatic pressure-controlled switches, designed to cut off any section with a bad air leak. His action at each of these was the same; from an outer pocket of his armor he would take a small wedge of steel and skillfully jam the door. It was this action which convinced Mayhew that the agent was not a scientist — he was displaying the skill of an experienced burglar or spy. He was apparently well supplied with the wedges, for in the hour before he found what he was seeking he jammed more than twenty of the air breaks. Mayhew and Floyd did not bother to have them cleared at the time, since no one was in the outer level without a spacesuit.
Nearly half of the outer level was thus unified when Hart reached a section of corridor bearing valve handles and hose connections instead of doors, and knew there must be liquids behind the walls. There were code indexes stenciled over the valves, which meant nothing to the spy; but he carefully manipulated one of the two handles to let a little fluid into the corridor, and sniffed at it cautiously through the gingerly cracked face plate of his helmet. He was satisfied with the results; the liquid was one of the low-volatility hydrocarbons used with liquid oxygen as a fuel to provide the moderate acceleration demanded by space launched torpedoes. They were cheap, fairly dense, and their low-vapor pressure simplified the storage problem in open-space stations.
All that Hart really knew about it was that the stuff would burn as long as there was oxygen. Well — he grinned again at the thought — there would be oxygen for a while; until the compressed, blazing combustion gases blew the heat-softened metal of the outer wall into space. After that there would be none, except perhaps in the central core, where the heavy concentration of radioactive matter made it certain there would be no one to breathe it.
At present, of course, the second level and any other intermediate ones were still sealed; but that could and would be remedied. In any case, the blast of the liberated fuel would probably take care of the relatively flimsy inner walls. He did not at the time realize that these were of magnesium, or he would have felt even more sure of the results.
He looked along the corridor. As far as the curvature of the outer shell permitted him to see, the valves projected from the wall at intervals of a few yards. Each valve had a small electric pump, designed to force air into the tank behind it to drive the liquid out by pressure, since there was no gravity. Hart did not consider this point at all; a brief test showed him that the liquid did flow when the valve was on, and that was enough for him. Hanging poised beside the first handle, he took an object from still another pocket of his spacesuit, and checked it carefully, finally clipping it to an outside belt where it could easily be reached.
At the sight of this item of apparatus, Floyd almost suffered a stroke.
“That's an incendiary bomb!” he gasped aloud. “We can't possibly take him in time to stop his setting it off which he'll do the instant he sees our men! And he already has free fuel in the corridor!”
He was perfectly correct; the agent was proceeding from valve to valve in long glides, pausing at each just long enough to turn it full on and to scatter the balloon-like mass of escaping liquid with a sweep of his arm. Gobbets and droplets of the inflammable stuff sailed lazily hither and yon through the air in his wake.
Mayhew calmly lighted a cigarette, unmindful of the weird appearance of the match flame driven toward his feet by the draft from the ceiling ventilators, and declined to move otherwise. “Decidedly, no physicist,” he murmured. “I suppose that's just as well — it's the military information the army likes anyway. They certainly wouldn't have risked a researcher on this sort of job, so I never really did have a chance to get anything I wanted from him.”
“But what are we going to do?” Floyd was almost frantic. “There's enough available energy loose in that
