"Maybe not," said Tom. "Remember, the order for us to report back was signed by Commander Walters, not the cadet supervisor of leaves. I think that means something special." Suddenly the monorail roared out of the tunnel and into brilliant early-morning sun again. The three cadets turned quickly, their eyes sweeping the valley for the first sight of the shining Tower of Galileo. "There it is," said Tom, pointing toward a towering crystal building reflecting the morning light. "We'll be there in a minute." Even as Tom spoke, the speed of the monorail slackened as it eased past a few gleaming structures of aluminum and concrete. Presently the white platform of the Academy station drifted past the viewport and all forward motion stopped. The doors opened and the three boys hurried to the exit. All around the cadets, men and women in the vari-colored uniforms of the Solar Guard hurried through the station. The green of the Earthworm cadets, first-year students of the Cadet Corps; the brilliant rich blue of the senior cadets like the _Polaris_ unit; the scarlet red of the enlisted Solar Guard; and here and there, the black and gold of the officers of the Solar Guard. The three cadets hurried to the nearest slidewalk, a moving belt of plastic that glided silently across the ground toward Space Academy. It whisked them quickly past the few buildings nestled around the monorail station and rounded a curve. The three cadets looked up together at the gleaming Tower of Galileo. Made of pure Titan crystal, it soared above the cluster of buildings that surrounded the grassy quadrangle and dominated Space Academy like a translucent giant. The cadets stepped off the slidewalk as it glided past the Tower building and ran up the broad marble stair. At the huge main portal, Tom stopped and looked back over the Academy grounds. All around him lay the evidence of mankind's progress. It was the year 2353, when Earthman had long since colonized the inner planets, Mars and Venus, and the three large satellites, Moon of Earth, Ganymede of Jupiter, and Titan of Saturn. It was the age of space travel; of the Solar Alliance, a unified society of billions of people who lived in peace with one another, though sprawled throughout the universe; and the Solar Guard, the might of the Solar Alliance and the defender of interplanetary peace. All these things Tom saw as he stood in the wide portal of the Tower Building, flanked by Astro and Roger. Turning into the Tower, the three cadets went directly to the office of their unit commander. The training program at Space Academy consisted of three cadets to a unit, with a Solar Guard officer as their teacher and instructor. Steve Strong, captain in the Solar Guard, had been their cadet instructor since the unit had been formed and he now smiled a welcome as the cadets snapped to attention in front of his desk.