Father Damien Karras: 'Where is Regan'. Regan MacNeil: 'In here. With us'. The terror begins unobtrusively. Noises in Regan's room, an odd smell, the displacement of furniture, an icy chill. Easy explanations are offered. Then frightening changes start in the eleven-year-old girl. Medical tests shed no light on her symptoms, but it is as if a different personality has invaded the child. Father Damien Karras, a Jesuit priest, is called in. Is it possible that a demonic force is present in the child? Exorcism is the only answer...