Ignoring Exorcist II: The Heretic, this one deals with a serial killer who was executed the same night of the exorcism in the first film with the girl Regan. The priest who fell down the flight of steps was been taken into the spirit of the killer to claim victim after victim some 20 years later. The killer mutilates priests and doctors and uses old women as a suspect. After the returning police detective Kinderman sees that it is the same serial killings of the Gemini, he and another priest decide to find and destroy the killer's spirit with using the final exorcism. But this exorcism will be much dangerous...