If next year people try to determine the worst ending of any picture in the last twelve months, “The Devil Inside” will probably cop the prize easily. Like “Seven Days in Utopia,” it turns the movie into a virtual advertisement for a website—except that it’s an ad you have to pay to watch. That’s hardly a good deal.

If Hollywood is anything to go by, there must be more cases of demonic possession than there are baptisms and marriages (only one of which is to be found here, and it turns out badly, too). This picture is latest evidence, a poverty-row horror picture that, like “The Last Exorcism” (a title that sadly proved less than prophetic), applies the fly-on-the-wall documentary technique of “The Blair Witch Project” to the subject.

Of course there has to be a set-up, and in this case it’s a faux police-investigation tape of a terrible murder scene twenty years earlier. A psychologically troubled woman, Maria Rossi (Susan Crowley), confessed to brutally killing three people—who turn out to have been two priests and a nun from her parish who were trying to perform a presumably unauthorized exorcism on her.

Jump ahead a couple of decades and Maria’s daughter Isabella (Fernanda Andrade) is determined to discover the truth about her mother, who was found insane and eventually transported to an asylum in Rome. She’s accompanied there by filmmaker Michael (Ionut Grama), who will document her odyssey.

Isabella winds up in an exorcism class at the Vatican, where she meets a couple of young priests—Ben (Simon Quarterman) and David (Evan Helmuth), who are disaffected over official policy of dismissing most possession cases as psychologically-based and are themselves performing “private” rituals on afflicted people like Rosa (Bonnie Morgan), who has a single Linda-Blair type scene to sate the audience’s early expectations.

But the crew soon move on to Maria in a sequence that gives Crowley the opportunity to go berserk in full scenery-chewing mode. And it turns out that not only is she suffering from possession by multiple demons (think back to a bit of dialogue from that Vatican class session!) but the demons can jump from one person to another in a fashion similar to the technique the alien used in “The Thing” and the demons in “Supernatural” (reference that Vatican lecture again). This does not bode well for our intrepid quartet, who are all threatened with possession themselves. They suffer all sorts of preternatural attacks before—well, before the picture literally comes to a screeching halt without bothering to come to any resolution. Viewers are likely to feel cheated—and they have every right to be.

To be fair, “The Devil Inside” does manage some effective shocks—it’s difficult not to, what with scenes involving gruesomely butchered bodies, zombified people doing contortionist tricks, and sudden spurts of violence (though the very first one is that hoariest of cliches in which the characters are spooked by a snarling dog leaping at them from out of frame). The faux-documentary footage is less irritatingly jittery than is usual in this brand of flick (modest kudos to cinematographer Gonzalo Amat). And the acting, though hardly of award caliber, is a notch above what one customarily encounters in cheap horror movies—testimony to the cast’s dedication to the inferior material and the hand of director William Brent Bell.

But “The Devil Inside” ultimately proves a tired riff on an old formula that loses steam even before its atrocious ending. Paramount obviously picked the movie up in the hope it might duplicate the success of its el-cheapo cult sensation “Paranormal Activity.” There’s about as much chance of that happening as of your encountering a real exorcism. The Vatican, however, far from being displeased with the picture, should actually embrace it. After all, its message appears to be that rituals that don’t bear its sanction are bound to end disastrously. In other words, it’s not nice to fool with Holy Mother Church.