A young science fiction fan is accidentally brought to the planet Kor-Am to save its people from a strange menace, and he figures out the solution that had eluded them.; The Knights meet a race of hostile mole-people from an underground civilization.; The mole-people are defeated because of their aversion to light. Later, Douglas reveals his discovery that the mole-people's first step in their plan was six years earlier when they began the nuclear war that destroyed most life on Earth.