Incubus

The summer peacefulness of the New England community of Galen is suddenly shattered by a series of murders. Dr. Sam Cordell (John Cassavetes), a newly arrived surgeon and pathologist, tries to help veteran police chief Hank Walden (John Ireland) investigate the baffling crimes. Jenny, Dr. Cordell's daughter, tells her father about the terrible recurring nightmares suffered by her boyfriend, Tim Galen, which seem to coincide with the slayings. At the town museum, scene of one of the murders, Dr. Cordell finds an ancient book that tells of Incubus, a demon of many forms that ravishes women in their nightmares. He also learns that Incubus and Succubus, a demon that appears to men, can be sexually interchangeable. In the film's shocking and terrifying climax, Dr. Cordell monitors Tim's nightmare, taking him through to the awful realization of what the Incubus is and who it is in human form. (official distributor synopsis)