When exobiologist Jules Rammis returns to Earth after saving the Terran colony on planet Tartarus from a demented member of the Loranth race, he hopes to spend some quiet time with his five-year-old daughter Lisa, whom, he finds, has inherited his own telepathic skills. But a powerful denizen of planet Halcyon summons them both to his pristine world to destroy a Terran ravager, the Dream Czar of Halcyon. Jules demands to know why his daughter should be involved in this murderous plot. The alien responds that human telepaths are rare, and that he needs them for his plan. When Jules refuses to take Lisa on such a dangerous mission, the infuriated alien threatens to kill them both and destroy the treacherous community of Terrans on Halcyon. Given no choice, Jules takes Lisa aboard a spaceship headed for Halcyon. But the prospect of exposing his young daughter to unknown dangers keeps Jules more anxious than when he faced the Loranth of Tartarus.