The 1981 movie Incubus is directed by John Hough, who is notable for his many genre films including: Twins of Evil (1971), The Legend of Hell House (1973), Dirty Mary, Crazy Larry (1974), Escape to Witch Mountain (1975), and American Gothic (1988). If my memory is correct, I believe this is one of many Canadian produced films from the late 1970s/early 1980s that was made possible by lucrative government sponsored tax breaks.
The film is based on a 1976 novel by Ray Russell, who aside from being a prolific author also served as co-screenwriter on Roger Corman films such as X: The Man With the X-Ray Eyes and The Premature Burial. The story is set in a small town that is shocked by a series of brutally violent rapes and murders which appear to be committed by either a gang of perpetrators or one very large evildoer. John Cassavetes is a local doctor who begins to suspect that a troubled young man, who much to his chagrin also happens to be dating his teenaged daughter, is somehow connected to the vicious assaults. Stick with the film until the end and you'll be rewarded with a curious twist ending.
Also of note is the appearance of a pre-Iron Maiden Bruce Dickinson. When a doomed gal goes on a date to the movies, the film being screened is a 1980 short directed by Julien Temple titled Biceps of Steel which features Dickinson with his earlier band Samson in a laughably dated laser and hard rock spectacle.