The Reverend Cotton Marcus is called to a farm belonging to Louis Sweetwer in rural Louisiana. He expects that he will just have to perform a routine 'exorcism' on another deranged religious fanatic. Sweetzer is a dedicated fundamentalist who has turned to Marcus as a last resort because he is convinced that his daughter Nell really is possessed by a demon. Marcus decides that he produce a documentary of this, his last exorcism, a confessionary film to absolve himself of his sins after not being able to deal with the years of scamming his fellow believers out of a great deal of money. However, this particular exorcism, his last one, just so happens to be different to normal, wherein the subject, Nell, really does seem to have an evil spirit of some sort within her, that threatens to destroy everyone on the farm.
