Incubus
Tags: allegory, revenge, romantic

Plot synopsis:
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.
Sam's teenaged daughter, Jenny, is dating Tim, but he disapproves of their relationship. At the hospital, Sheriff Hank Walden (John Ireland) questions Sam about Mandy's 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.
Attempts to question the comatose Mandy about her attacker are futile. Sam shows Laura pictures of his deceased 2nd wife and their amazing resemblance to each other. The following day, local farmer Ernie Barnes and his two daughters are brutally slain at their farmhouse. Tim again is tormented by his vision, and runs into a local movie theater in an attempt to distract himself. While there, a young woman is raped and murdered in the downstairs bathroom of the theater, and the metal stall door is found nearly bent in half. Sheriff Walden and Sam arrive at the crime scene shortly before Laura, who insists she may be able to help the investigation. She confides in Sam that she discovered historical records detailing Satanism and similar crimes occurring throughout the town's history.
Tim confronts Jenny at her home, hysterical, and says he believes his dreams are responsible for the crimes. Sam gets a sample of Tim's semen to compare against that which was found inside the victims, but they do not match. Tim and Agatha meet with Sam, Jenny, Laura, and Sheriff Walden at the library that night, where Laura reads a passage from a book detailing the shapeshifter known as the incubus, which manifests through dreams and can appear in human form. Agatha reveals that Tim's mother had died before his birth and had been accused of witchcraft due to psychic powers she possessed; Agatha claims that the Galen family has a legacy of witch hunters, and that his dreams are a result of this.
Laura and Tim return with Sam and Jenny to their home. As Laura takes Jenny upstairs to go to bed, Sam attempts to induce Tim's dream to prove its connection to the murders. Tim goes into a seizure-like state and runs upstairs into Jenny's room where he tries to attack Laura with a dagger given to him by Agatha, but Sam intervenes and stabs him to death. Laura then approaches Sam, and her face briefly shifts into that of the monstrous incubus; it is revealed that Laura has in fact been the incubus all along, manifesting in female form. As Laura embraces Sam, he looks over her shoulder to see Jenny's dead body lying on her bed, blood pouring out from between her legs.