Tom Corbett, Roger Manning, and the big Venusian Astro have triumphed over the perils of interplanetary pirates, rogue reactors, and hostile environments. But when the Polaris is assigned to lead a "wagon train" of ships to colonize a distant world, the cadets find themselves in a dangerous situation that could finally signal the end of the "best unit" in the Academy. After Captain Strong abruptly departs under strange circumstances, Tom and his pals get entangled in a secret plot involving a belligerent scientist, a suspicious politician, and a planetary anomaly that crashes spaceships. And now the clock is ticking: the cadets can either solve this mystery fast ... or face some truly unpleasant consequences. (Book 4 in the Tom Corbet, Space Cadet series)