The Exorcist is a novel of supernatural suspense by William Peter Blatty in 1971. It was by a 1949 case of demonic possession and exorcism that Blatty heard about while he was a student in the class of 1950 at Georgetown University, a Jesuit school.
Aspect of the character Father Merrin were based on the British archaelogist Gerald Lankaster Harding, who had excavated the caves where the Dead Sea Scrolls had been found and whom Blatty had met in Beirut. Blatty has stated that Harding was the physical model in his mind when he created the character.
The story begins when an elderly Jesuit priest named Father Lankaster Merrin is leading an archaelogical dig in northern Iraq and is studying ancient relics. Following the discovery of a small statue of the demon Pazuzu (an actual ancient Assyrian demigod) and a modern day St. Joseph medal curriously justapoxed together at the site, a series of omens alerts him to a pending confrontation with a powerfull evil, which unknown to the reader at this point, he has battled before in an axorcism in Africa.
Meanwhile, in Georgetown, a young girl named Regan MacNeil living with her famous mother, actress Chris MacNeil, becomes inexplicably ill. After a gradual series of poltergeist-like disturbances, she undergoes disturbing psychological and physical changes, appearing to become “possessed” by a demonic spirit.
After several unsuccesful psychiatric and medical treatments, Regan’s mother turns to a local Jesuit priest. Father Damien Karras, who is currently going through a crisis of faith coupled with the loss of his mother, agrees to see Regan as a psychiatrist, but initially resist the nation that it is an actual demonic possession inhabited by a diabolical personality, he turns to the local bishop for permission to perform an exorcism on the child.
The bishop with whom he consults does not believe Karras is qualified to perform the rites, and appoints the experienced Merrin, recently returned to the States, to perform the exorcism; although he does allow the dourbt-ridden Karras to assist him. The lengthy exorcism tests the priests both physically and spiritually. After the death of Merrin, who had previously suffered cardiac arrhythmia, the task ultimately falls upon Father Karras. When he demands that the demonic spirit inhabit him instead of the innocent Regan, the demon seizes the opportunity to afflict the priest, thus Karras surrenders his own life in exchange for Regan’s.