The Exorcist by William Peter Blatty
The Exorcist is a horror novel written by William Peter Blatty. It is based on a 1949 exorcism Blatty heard about while he was a student in the class of 1950 at Georgetown University, a Jesuit and Catholic school. The exorcism was purportedly performed in Mount Rainier, Maryland.
This unstoppable publishing phenomenon was the inspiration behind one of the most successful horror movies of all time. A powerful presence has taken possession of the 12-year-old daughter of a film star. The ensuing battle between a doubt-ridden priest and the unspeakable horror within the girl is a classic war of good versus evil.