Buckling under the weight of his conscience after years of making money by performing fake exorcisms for religious fanatics, Reverend Cotton Marcus decides to film a confessionary documentary of his last exorcism. But when he arrives on the rural Louisiana farm of Louis Sweetzer, whose daughter Nell is possessed, it is soon clear that nothing could have prepared him for the true evil he encounters there. Now, too late to turn back, Reverend Marcus' own beliefs are shaken to the core when he and his crew must find a way to save Nell - and themselves - before it is too late.