When she is a young girl, Rose Tierney, with a group of teenagers, sneaks off to a deserted, reputedly haunted house. During a séance in the house, a spirit speaks and says that it pervades the house. When the young girl is locked by accident in a room in the house, she senses that an unseen spirit is raping her and inhabiting her body.
After Rose, as an adult, is mugged in New York City, she begins to experience out-of-body traveling and gradually learns that she has been raped by the parasitic form of an occultist, Peter Grace, who, through her, sought psychic immortality. The implications are subtle and terrifying, as Rose comes to learn that the world is gradually being dominated by occultists.
One such person is Rose’s neighbor, Colin, who deceives her and pretends to be her friend and adviser, until his true nature is revealed in the final scenes. Rose’s husband, Bill, becomes a member of the occultist class as the parasite takes over his body. In an almost-too-clever plot twist, Rose is reunited with Bill after the trauma apparently has ended. She becomes pregnant with his child. At the beginning of her labor, Colin appears again (he was presumed killed in a car accident), and Rose realizes that she is giving birth to a new life containing the parasite. She finally kills herself, thereby killing the spirit of Peter Grace.