Greg grinned to himself. He thought of the months of conditioning he had gone through to prepare for this run ... the hours in the centrifuge to build up his tolerance to accelleration, the careful diet, the rigorous hours of physical conditioning. It was only one experiment, one tiny step in the work that could someday give men the stars, but to Gregory Hunter at this moment it was everything. "Good luck, then." The captain cut off, and the blastoff buzzer sounded. He was off. His heart hammered in his throat, and his eyes ached fiercely, but he paid no attention. His finger crept to the air-speed indicator, then to the cut-off switch. When the pressure became too great, when he began to black out, he would press it. But not yet. It was speed they wanted; they had to know how much accelleration a man could take for how long and still survive, and now it was up to him to show them. Fleetingly, he thought of Tom ... poor old stick-in-the-mud Tom, working away in his grubby little Mars-bound laboratory, watching bacteria grow. Tom could never have qualified for a job like this. Tom couldn't even go into free-fall for ten minutes without getting sick all over the place. Greg felt a surge of pity for his brother, and then a twinge of malicious anticipation. Wait until Tom heard the reports on _this_ run! It was all right to spend your time poking around with bottles and test tubes if you couldn't do anything else, but it took something special to pilot an XP ship for Project Star-Jump. And after this run was over, even Tom would have to admit it.... There was a lurch, and quite suddenly the enormous pressure was gone. Something was wrong. He hadn't pushed the cut-off button, yet the ship's engines were suddenly silent. He jabbed at the power switch. Nothing happened. Then the side-jets sputted, and he was slammed sideways into the cot. He snapped on the radio speaker. "Control ... can you hear me? Something's gone wrong out here...." "Nothing's wrong," the captain's voice said in his earphones. "Just sit tight. I'm bringing you back in. There's a call here from Sun Lake City. They want you down there in a hurry. We'll have to scratch you on this run." "_Who_ wants me down there?" "The U.N. Council office. Signed by Major Briarton himself and I can't argue with the Major. We're bringing you in." Greg Hunter sank back, disappointment so thick he could taste it in his mouth. Sun Lake City! That meant two days at least, one down, one back, maybe more if connections weren't right. It meant that the captain would send Morton or one of the others out in his place. It meant.... Suddenly he thought of what else it meant, and a chill ran up his back. There was only one reason Major Briarton would call him in like this. Something had happened to Dad. Greg leaned back in the cot, suddenly tense, as a thousand frightful possibilities flooded his mind. It could only mean that Dad was in some kind of trouble.