Comparisons to The Blair Witch Project (1999) and last year’s Paranormal Activity are the inescapable fate of Daniel Stamm’s The Last Exorcism, if only because all three movies employ a similar ruse: they are scary stories masquerading as vérité snuff. And there’s nothing scarier than the idea, fueled by a bogus Internet rumor, that the bogeyman this time is real.

Exorcism seems in one way less gimmick-driven than the others, since it doesn’t arrive on the heels of a viral campaign touting its authenticity. Yet it comes across as the genuine article – we’re not fooled, exactly, but we are willing to believe. The story earns credibility.

Whether more exorcisms are performed today than at any time in recorded history, as evangelical huckster Cotton Marcus (Patrick Fabian, of HBO’s Big Love) tells us early on, is not something I’m qualified to dispute, but it wouldn’t surprise me. It stands to reason that the ritual gained a certain cachet from William Friedkin’s 1973 classic The Exorcist, and that perceptions of what the ancient practice entails have been irrevocably shaped by a movie.

Marcus himself acknowledges this, but he is no Father Karras, and Stamm’s tense, suspenseful thriller bears little resemblance to The Exorcist. Produced by Hostel director Eli Roth, Exorcism is no vomitorium, as its PG-13 rating attests. It is, rather, a cerebral journey into the world of religious fanaticism, where Marcus, a skeptic, foolishly chooses to tread.

This is a movie, unlike Blair Witch and Paranormal Activity, in which characters never surrender their intelligence in the service of an idiot plot. Yet when Marcus and his camera crew realize they’ve wandered into a situation they can neither understand nor control, they don’t simply flee. Why not?

Partly, it’s ego. Marcus, a veteran preacher, knows how to keep a congregation in the palm of his hand – to prove it, he slips his mother’s banana bread recipe into one of his rowdy sermons. (Nobody notices.) Staunchly secular, he sees worldly solutions to the supposedly supernatural crises around him, and never do those solutions seem like a stretch. His assumptions and reactions are plausible.

Marcus, like Fabian, never makes a false move. Neither does Stamm (director of the equally disturbing A Necessary Death), who understands that what’s left off-screen is often more terrifying than what’s on it.

And I must not disclose what that is, since to appreciate the full impact of The Last Exorcism is to not know what’s coming. The movie plays its audience like a piano, and that chilling last note is a shocker.