The terror began so unobtrusively they might have forgotten all about it. Noises in Regan's room, an odd smell, misplaced furniture, an icy chill. Small annoyances for which Chris MacNeil Regan's actress mother, easily found plausible explanations.

The changes in eleven-year-old Regan were so gradual too that Chris, busy filming a new picture, did not recognize for some time how much her daughter's behavior had altered. And even when she did, the endless medical tests that followed had shed no light on Regan's symptoms, which grew increasingly severe and frightening. It was almost as if a different personality had invaded the little girl. The very house thickened with the sense of an evil presence.

Desperate, Chris turned from the doctor to Father Damien Karras, a Jesuit Priest who was trained as a psychiatrist and had also a deep knowledge of such phenomena as satanism and possession. Was it possible that a demonic force was at large? If psychiatry could not help, might exorcism be the answer?

Damien Karras resisted the idea. In its long history the Church has been profoundly skeptical of possession. But, finally, it came down to a matter of Regan's life or death. And that meant the time had come for that solemn and implacable rite that binds exorcist and demon in literally mortal combat.

No reader of this fantastic and deeply religious novel will come away untouched by the power of that ritual, or unaffected by those things in this world which cannot be explained by the most rational inquiry, the more informed skepticism.

Was Regan possessed?