Philip Lamont, a priest struggling with his faith, attempts to exorcise a possessed South American girl who claims to "heal the sick". However, the exorcism goes wrong and a lit candle sets fire to the girl's dress, killing her. Afterwards, Lamont is assigned by the Cardinal to investigate the death of Father Lankester Merrin, who had been killed four years earlier in the course of exorcising the Assyrian demon Pazuzu from Regan MacNeil. The Cardinal informs Lamont that Merrin is facing posthumous heresy charges because of his controversial writings as Church authorities are trying to modernize and do not want to acknowledge that Satan exists.