The Incubus (1982 film)

The Incubus also known simply as Incubus is a 1982 American horror film directed by John Hough, and starring John Cassavetes, Kerrie Keane, and John Ireland. The plot focuses on a small New England town where a mysterious figure is raping and murdering young women. The film was written by George Franklin, and based on the novel of the same name by Ray Russell.

In a lake at a rock quarry, a young woman named Mandy and her boyfriend, Ray, are swimming. The two spend the night at the lake camping, but are attacked by an unseen figure Ray is killed, and Mandy is taken to the hospital with a ruptured uterus and serious trauma. As the attack occurs, teenager Tim Galen experiences a recurring nightmare he has in which a woman is tortured by a monstrous figure his grandmother, Agatha Galen, tries to dissuade him of his suspicions about the premonitory dream. At the hospital, Mandy is treated by Sam Cordell John Cassavetes, a surgeon and physician in the small community of Galen.Sams teenaged daughter, Jenny, is dating Tim, but he disapproves of their relationship. At the hospital, Sheriff Hank Walden John Ireland questions Sam about Mandys injuries, and a nosy local reporter, Laura Kincaid, arrives to question Walden, who forces her to leave. That night at the local library and museum, a librarian named Carolyn Davies is brutally raped and murdered while closing the building. During her autopsy, Sam finds she suffered similar wounds as Mandy, and finds an inexplicable amount of semen in her vagina. ........

Source: Wikipedia