The Exorcist is a supernatural horror film based on the 1971 novel of the same name by William Peter Blatty. The movie follows the story of Regan MacNeil (Linda Blair), a 12-year-old girl who begins to exhibit strange behavior, such as convulsions, unexplained noises, and a significant change in personality. Her mother, Chris MacNeil (Ellen Burstyn), becomes increasingly concerned and seeks medical help, but as Regan's behavior becomes more erratic, it becomes clear that something more sinister is at play.