When the twelve-year-old daughter of actress Chris MacNeil begins to behave in an increasingly violent and inexplicable way, the desperate mother turns first to doctors and, with science exhausted, to the Church. Father Karras, a young Jesuit shaken by a crisis of faith, and the veteran exorcist Father Merrin then confront a demonic entity that has taken possession of the girl's body in a terrible duel for her soul. Directed by William Friedkin, it is one of the most influential horror films in history, a disturbing descent that still retains its power to unnerve.