Tonight I saw The Last Exorcism, starring Patrick Fabian and Ashley Bell.
Cotton Marcus (Fabian) is a Southern reverend who claims more to be a trained actor than a genuine voice of God. He agrees to let a film crew create a documentary about his "last exorcism" so he can expose all of his tricks and reveal the practice to be a universal sham.
His subject is a 16-year-old farm girl named Nell (Bell). She seems sweet enough during the daytime, but at night her Bible-bouncing father reports that demons emerge and she kills random pets/livestock.
With her father and brother as witnesses, Cotton performs his "exorcism" complete with fake sounds and a shaking bed, which he controls with fish wire. He proclaims the demons gone and leaves with a fat paycheck to a nearby motel.
Unfortunately, something is still the matter with Nell and she materializes at the motel, desperately in need of assistance. Cotton and the filmmakers take her to a hospital, but once she returns home, they learn she's hurt her brother. After another hospital trip, the reverend tries to convince the father to get her psychiatric help, but he doesn't believe in it.
Cotton (who really turns out to be somewhat of a decent fellow) feels responsible for Nell in some way, so he decides to help her himself and keeps digging to learn the truth.
The film is perfectly enjoyable/believable up to this point, then it all takes a turn for the worse.
One minor twist leads to a few different theories about Nell's evil, then the answer is given to us in an ending that makes you doubt the same screenwriter wrote the first half of the film.
The script did an excellent job of building the suspense and wonder through well-developed, complex characters and then left us alone with a convention that's been overused since film was invented.
What a shame.