Directed by William Peter Blatty, the film follows a police lieutenant investigating a series of murders with similarities to a previously executed killer. As the investigation develops, connections emerge to events linked to earlier cases, bringing together criminal inquiry and supernatural elements. The film is part of The Exorcist series and adapts Blatty’s novel Legion.

Från IMDB:
A police lieutenant uncovers more than he bargained for as his investigation of a series of murders, which have all the hallmarks of the deceased Gemini serial killer, leads him to question the patients of a psychiatric ward.