Chris MacNeil, a very famous young actress, has noticed several behavior changes in her 12 year old daughter, Regan. It started when Regan complained her bed was shaking, but then the problems gradually got more serious, such as Regan vomiting green slime on a local Jesuit priest, and her turning her head completely around.
As problems grew worse, Chris exhausted option after option, until an exorcism was all that was left to do.
She called the local Jesuit Father Karras to perform an exorcism, but the Bishop said that it should be done by someone with more experience than Karras. Father Merrin was later contacted, then arrived in Georgetown to perform the exorcism.
When he and Karras walked into Regan's bedroom to begin, Regan yelled several funny phrases at him such as these
'Your mother sucks cocks in Hell'
'Stick your cock up her ass you motherfucking worthless COCKSUCKER!!!'
Later on in the exorcism, father Merrin dies of heart failure, and Karras finishes the exorcism by letting Pazuzu come into him, then throws himself out of Regan's window, falling down a flight of steps.
The film ends with Regan and Chris moving out of the house in which she was posessed.