Regan McNeil, a twelve-year old girl and her mother Chris seem as happy as can be. But, Regan soon appears to get sicker and sicker, exhibiting strange behavior and changing appearance. Deeply concerned Chris seeks help on a medical level, but the doctors have no answers. Meanwhile, things on the home front turn darker, the room is freezing, books are flying around at will and something "not so normal" has taken over sweet little Regan. Seeking help from the church directly seems pointless. Father Damien Karras is called to help point out the words carved on Regan's stomach. Karras then makes a conscious decision to get this situation rectified. Under the leadership of Father Merrin the two priests delve into the relative unknown. One priest must use ever shred of devotion he can muster while the elder priest must fight for his very own life and fight off his own demons. As expected good conquers evil but not before the demon plays his trump cards, using the priests weaknesses to try and break them. Two priests go in, one comes out and Regan is left with no memory of the events.