His brown curly hair falling over his forehead, Tom Corbett frowned in concentration as he kept the earphones of his study machine clamped tightly to his ears and listened to a recorded lecture on astrophysics as it unreeled from the spinning study spool. As command cadet of the _Polaris_ unit, Tom was required to know more than merely his particular duty as pilot of a rocket ship. He had to be familiar with every phase of space travel, with a working knowledge of the duties of all his unit mates. Astro, the power-deck officer of the unit, paced back and forth between the bunks like a huge, hulking bear, muttering to himself as he tried to memorize the table of reaction times for rocket motors. Though the huge Venusian cadet was a genius at all mechanical tasks, and able to work with tools the way a surgeon worked with instruments, he had great difficulty in learning the theories and scientific reasons for all the things he did instinctively. Suddenly Astro stopped, looked at his chronometer, then turned to Tom. "Hey, Tom!" he called. "Where's that jerk, Manning?" "Huh?" replied Tom, lifting one of the earphones from his ears. "What did you say, Astro?" "Where's Manning?" reiterated Astro. "It's ten minutes after lights out." "He was going to get those study spools for us, wasn't he?" mused Tom. "He should've been back by now," grunted the Venusian. "The library closed an hour ago. Besides, he couldn't have gotten those spools. Every other cadet in the Academy is after them." "Well, he's a pretty resourceful joker," sighed Tom, turning back to the study machine. "When he goes after something, he gets it by hook or crook." "It's the crook part that bothers me," grumbled Astro. "Besides, if the O.D. catches him out of quarters, he'll be doing his studying while he's polishing up the mess hall." Suddenly the door to the room burst open and slammed closed. Tom and Astro whirled to see their missing unit mate lounging against the doorframe, grinning broadly. "Roger!" "Where've you been, blast you?" Tom and Astro both jumped forward and spoke at the same time. The blond-haired cadet merely looked at them lazily and then sauntered forward, pulling six small study spools from his pockets. "You wanted these study spools, didn't you?" he drawled, giving his unit mates three apiece. "Be my guest and study like mad." Tom and Astro quickly read the titles of the spools and then looked at Roger in amazement. They were the ones the unit needed for their end-term exams, the ones all the cadets needed. "Roger," Tom demanded, "how did you get these spools? The library was out of them this afternoon. Did you take them from another unit's quarters?" "I did not!" said Roger stoutly. "And I don't like your insinuations that I would." He grinned. "Relax! We have them and we can breeze through them in the morning and have them back where they belong by noon tomorrow." "Where they belong!" Tom exclaimed. "Then you have no right to them."