When originally published in 1971, The Exorcist became not only a bestselling literary phenomenon, but one of the most frightening and controversial novels ever written. (When the author adapted his book to the screen two years later, it then became one of the most terrifying movies ever made.) Blatty fictionalized the alledgeded true story of a child's demonic possession in the 1940s. Of course, it is still jus a book :)