Cyd Brougham is an investigative journalist staying at a hotel in the Rocky Mountains. The object of her scrutiny? A mysterious and secretive man named Percy Clerkenwell. Throughout her stay, however, a more interesting occurrance emerges. Several women are sexually violated, and each one claims that the purpotrator was a purple monster, who has the ability to become invisible. At one point, Cyd herself becomes victim to the creature's rapes, which motivates her to double down on Clerkenwell.
Her hunch is correct. After getting herself captured, Clerkenwell reveals to her that he discovered and befriended the creature, which he explains is an alien from a distant planet. He further divulges that he and the alien communicate telepathically, and that the creature benefits from the partnership by getting food and shelter, while Clerkenwell benefits by getting to feel the exact same sexual sensations whenever the alien climaxes.
Naturally, revealing this was a dumb move. Cyd attempts to mentally communicate with the alien, succeeds, and orders the alien to kill Clerkenwell, but not before revealing some intentions of her own: She plans to use the alien to steal classified information from all the governments of the world.