Even by the degraded standards of early-'80s slasher films, The Incubus is pretty hard to sit through. A grumpy John Cassavetes plays a small-town doctor investigating a series of sex murders with a supernatural twist; the only other name actor is John Ireland, and everybody else is atrocious. Most of the genre's conventions are trotted out, albeit at a glacial pace: shower scene, young couple swimming at an isolated lake. The one quirky element, a suggestion of unhealthy intimacy between Cassavetes and his teenage daughter, might have creepy potential if it weren't so obviously a red herring. To his credit, Cassavetes passes through the entire film looking as though he would like to disappear into a corner. This low-budget Canadian offering is not to be confused with Incubus, the daffy William Shatner picture shot in the language of Esperanto, which is actually pretty fun.