With a few minutes to spare, he could tune the tube he'd designed as a weapon, and spray them with that. Its straight-line efficiency would insure that no dangerous amount of its radiation would reach the men two thousand miles away. Vengeance was his for the taking. He reached for the other tube, hesitated, and picked up a piece of paper and a pencil. The men at the base had the working plans of his device by now. They had to be warned how dangerous it would be not to make absolutely sure that their radiation generators and detectors couldn't spill dangerous radiation at random. Also that the Aliens could detect an inefficient search ray. Norden headed for the flexible seal at a full run, while his steady hands pencilled the final information on the radiation frequencies needed. He broke through into the air of the entrance, yanked the diagrams off the pick-up rack, and snapped in the new instructions. He turned with a single motion, and headed for the workroom again. And stopped! Beyond the entrance, the gleaming fins of a rocket were visible. And the red light on the airlock indicated someone was coming through. As his eyes focussed, he saw the inner lock open, and Miles and Pat emerged in the red glare. They started to shout something, but he cut them off. "For God's sake, stay here. There's no air beyond. Alien ship!" He jumped through the seal. His hands swept up the tube that was to be a weapon, and his eyes darted to the screen. The pip was bigger now, and at maximum brightness. The Alien ship must be only tens of thousands of miles above, braking down to attack with deadly precision. Less than a hundred feet away, the two humans waited, at the mercy of any energy that might spill from his weapon! He would have to score with a perfect piece of marksmanship, with all the radiation directed in a straight line. The formulae of its propagation seemed like an endless belt in his mind. He tightened the helix of wire about the radio-active lode, trying to be sure they were even. With time, there were a number of things he might have done, but he had no time to spare. He might harm Miles and Pat--but the Alien beam would leave nothing to chance. The thought of Miles and Pat jolted through his mind in a delayed reaction. They'd seen him come into this airless space without a helmet. They knew now he wasn't human! Discovered! _Explode the ..._ "No!" he shouted silently into the airless room. He had to get the Alien first! He had no idea how much time he had left as he snapped a flashlight battery into place, and tried to line the weapon into resonance with the detector settings. He lifted his eyes, to stare up through the open roof of the building. He knew there should be a faint black dot in the sky, but he couldn't see it against the blackness of space.