At length, he drove himself to his feet. The plan, which had been hatched in the head office of the T.I.S., would brook no delay. Captain Cabot would have to wait. Stooping, he pulled a bundle of tough, specially-treated fiberoid, a material used in the construction of space suits, from under his bunk, slung it across his shoulder. Next, he dragged forth a clock-like instrument to which had been attached a magnesium flare, and lastly a cylinder of hydrogen. The hydrogen Gavin had refined from water by a crude electrolysis. The rest of the equipment he had slipped from the engine room, working on it during leisure moments since the little death. He opened his door. The corridor was deserted. Twice during the ascent topside, Gavin had to stop and rest. Even breathing was an effort. At length he reached the arched outer skin of the monster, pried open an escape hatch. The thick yellow air of Jupiter poured down upon him like soup. It smelled and tasted faintly like swamp gas. He had a momentary fear that he would strangle. A spasm of coughing seized him as he gulped in the first breaths. Then, his lungs having adjusted themselves, he clambered to the outer shell. A hundred feet below, he could make out the surface, only sketchily visible through the yellow pea-soup air. Slave pens and cantonments were all swallowed by the dense fog. He set to work assembling his instruments. The cold knifed to his bones. A wind was blowing, too. It pushed against him like the sluggish current of a river. The fiberoid package, unfolded, proved to be a balloon almost ten feet in diameter. It had a safety valve in it to neutralize the pressure when the bag reached the stratosphere. Gavin attached the clock and flare, started the clock in operation, inflated the bag. The instant it tugged at his numbed fingers, he shut off the hydrogen, cast it free. It was scarcely a fifth inflated, but the heavy pressure caused it to float slowly, upward out of sight. The clock was timed to ignite the flare when the balloon reached the stratosphere. Observatories on Io, Europa, Callisto, and Ganymede had their instruments trained on Jupiter. As soon as the flare was discovered, a check was to be made of the prevailing winds in that area. A simple parabola would indicate the balloon flare's probable course. The information then would be relayed to a flight of five patrol spacers held in readiness on the nearer moon. That was the way it had been planned. But now Gavin was not so sure. So many things could interfere. He closed the trap overhead and retreated back to his cabin. Sweating profusely, he flung himself on his bunk. He was still there, his breath rasping in his throat, when his door was pushed silently open from the outside. Gavin whipped his dart-gun from its spring clip and slipped it under his pillow. He didn't move, but lay still with his eyes closed except for the barest fraction of an inch. The door yawned wider.