Synopsis by Hal Erickson
The Jupiter 2 is inexorably drawn towards a planet ruled by a creature consisting of a blue mist, which is nourished by stark, raw, fear. In order to "feed" on the visitors from earth, the creature works overtime to terrorize Will (Billy Mumy), beginning with making the members of the Robinson family disappear, one by one, and planting the seeds of paranoia in the boy's mind. But when the creature is unable to strike fear into the heart of Will, its only recourse is to destroy the youngster--with a maddened Dr. Smith (Jonathan Harris) as the destroyer! This episode represents the only appearance of the Jupiter 2's much-talked-about power core.