Inspired by newspaper reports of a 13-year-old Maryland boy whose body was said to have been taken over by demonic forces. After a lengthily prologue that is nearly incomprehensible to anyone who hasn't read the book, the first half of the film develops the essential character relationships and establishes the crisis situation. Regan MacNeil (Linda Blair) is the adorable, almost-pubescent daughter of divorcee and well known movie star Christ MacNeil (Ellen Burstyn). But when she prophesies the death of her mother’s acquaintance and urinates in the front of a roomful of dinner guests, Christ starts to wonder what has “gotten into” her daughter. More odd behavior, and a wildly shaking bed, lands Regan in the hospital, where she is subjected to a battery of extremely invasive procedures best described medical pornography. A brain lesion is suspected, but the tests prove nothing. When Regan, supposedly under hypnosis, responds to the smug questions of a hospital shrink by grabbing his scrotum, it is recommended that Christ seek the Church’s help. She does, pleading with doubt-ridden Jesuit priest Damien Karras (Jason Miller) to perform an exorcism. The film’s second half culminates in an intense battle between Karras and Regan’s demonic possessor, after the more experienced exorcist on the scene, Father Merrin (Max von Sydow) dies in the struggle.