Massimo Oderisi, Mel Ferrer, a wealthy Rome aristocrat, faces a crisis at home as his adult daughter Ippolita Oderisi, Carla Gravina, has been paraplegic since a car accident at age 12 that also claimed her mother. Doctors diagnose the paralysis as psychosomatic—rooted in psychological trauma rather than a physical injury. Having depended on her father since the accident, Ippolita has developed deep attachment issues, which intensify when Massimo begins a relationship with a woman named Greta, Anita Strindberg.
Seeking help, Ippolita visits her uncle, Bishop Ascanio Oderisi, Arthur Kennedy, a Vatican cardinal who admits there’s little he can do but recommends a secular parapsychologist, Dr. Marcello Sinibaldi, Umberto Orsini. Dr. Sinibaldi believes Ippolita has strong extrasensory perception and proposes that her symptoms come from unconscious memories of past lives. Through hypnosis, he makes her relive the suppressed memories of her namesake ancestor—a witch executed by the Inquisition—whose memory appears to possess her.
From this past life, Ippolita is momentarily able to walk again, but the possession triggers a dissociative state during which she seduces and murders a tourist. The menace intensifies, and at a family dinner she is fully possessed, displaying astonishing telekinetic powers that even astonish the household. The demon’s presence is palpable, and the family reels from the sudden shift in Ippolita’s personality and abilities.
Dr. Sinibaldi remains skeptical of anything supernatural, arguing the phenomenon is purely scientific, while Massimo persists that there may be something beyond explanation. He seeks help from his brother, but Ascanio insists on church approval from higher authorities before any exorcism can proceed. Irene, Alida Valli, the family maid, hires a local mystic to perform an exorcism, only for Ippolita to expose him as a fraud and to drive him from her room. An exorcism attempted by Ascanio also fails, as the demon taunts the Cardinal for turning away when help was asked.
Revelations unfold: the demon explains that the ancestor renounced him at the dying moment, preventing him from taking the soul—and now he intends to complete the original plan of using Ippolita’s body to birth a child. The Vatican then authorizes Father Mittner, George Coulouris, to conduct a formal exorcism. The demon tries to thwart him with psychic manifestations and telepathic interference, even hinting that the unborn child would be his son—the Antichrist.
Mittner’s exorcism culminates in a tense chase to the Colosseum, where Ippolita is finally subdued by the sound of church bells. Massimo seizes the moment to force Ippolita’s hands against an iron cross, expelling the demon and its child from her body. Restored, Ippolita supports her brother and father as the dawn breaks, leaving the estate behind and stepping into a new morning together.
