The Earth Defense Directorate faces a crisis when nearly everyone becomes sick after eating poisoned food. An attempt is made to create an antidote but the plan is thwarted when the laboratory is sabotaged and an assassin positions his weapon at Dr. Huer. Buck Rogers, Wilma Deering and Major Duke Danton travel to the planet Vistula where the poisoned food was exported from and they find a world engaged in slave labor. Then they discover that a fanatical religious leader and slave trader named Kaleel poisons Earth's food supply in order to weaken their defenses. Meanwhile, Kaleel is secretly planning to conquer Earth from his mountain fortress while their defenses are incapacitated.