rated PG-13

Any storyteller who’s entrusted to convey a tale that hinges deeply on moral implication and theological ambiguity should probably understand that revelation, literally, is another word for apocalypse. Proof, so the wise man says, denies faith. For true believers, then, seeing would be the opposite of believing. It was a tree of knowledge, after all, from which they say Eve nicked her apple, and ever since, knowing has apparently been the losing half of the Faithfuls’ battle.

Daniel Stamm, director of “The Last Exorcism,” cultivates a thoroughly compelling mystery about whether a comely young southern blossom was overcome by the Prince of Lies, or was simply rendered stark-barking schizo by seclusion and abuse on her family’s broken down old farm. It should therefore come as little surprise to Stamm that audiences almost universally groan out loud when he deliberately reveals all the secrets in the final two minutes of the film.

Right up to that point, the work holds together fairly well. But, it turns out, debut efforts from freshman filmmakers can be very much like the innocent young things so often besieged in possession movies like this—so full of promise, so ripe for corruption. Presenting the story as an unprocessed “found footage” documentary may have saved Stamm some cash on lights, sets and crew, and allowed a certain sloppy elbow room to camouflage his rookie-tude. But even as obvious and generally contemptible as the format is, his direction doesn’t even quite live up to that conceit. Unable to resist lingering, implausible establishing shots and entirely inappropriate musical cues, he appears at times to forget even the simplest rules of the game. He sabotages any POV immediacy he may have been able to generate with the assets he did actually carry to the screen.

Which brings us to the characters, performances and writing. Through all the worn-out quaky-cam subterfuge, the character of charlatan preacher Cotton Marcus, a charismatic big-city, holy-rolling hustler, emerges as a startlingly nuanced and three-dimensional individual. Groomed from boyhood to spread the Lord’s good word to the people, he’s apparently done a great deal of decent things for his flock (while delivering them neatly from their hard-earned dollars.) Having realized he’s become more of a showman than a shaman, he’s simply spent too much time behind the curtain of his own show to believe in the magic anymore. Wholly resolute in the conviction of his doubt, and perfectly comfortable embracing the suburban practicalities of raising his hearing impaired son with his lovely wife, there’s not a single reason to disbelieve him as he invites a camera crew out to witness his “one last job.” He plans to out himself and those like him as petty Invisible String hucksters, and finally just chuck all the mystic hoo-ha and sell some real estate like a normal person.

The man is not just deftly conceived, but flawlessly brought to life by actor Patrick Fabian. Heretofore best known for his role as “that guy” in “that show,” he’s spent nigh on 20 years in the background of TV productions from “Arliss” to “Xena.” His casting may well have been the result of another financial decision, but Stamm hit gold with this guy. He brings a genuinely charismatic balance of smarm and charm, and as Cotton’s veneer begins to melt under the pressure of some truly horrible confrontations, Fabian is able to draw a surprisingly authentic empathy to the surface. As loathsome as Cotton may be, Fabian allows us to believe he really does want to do good in the world. It’s an impressive hat-trick.

The intriguing, elusive characterizations don’t end there. The afflicted girl’s Pa, Louis (Louis Herthum), is a wonderfully realized inversion of Cotton—a small-town cracker of little education but of stalwart, if a shade medieval, principle. His son Caleb (Caleb Landry Jones) is a delightfully slippery and inscrutable figure who’s given woefully too little screen time. Little Nell (Ashley Bell), as the potentially demon-infused center of all the hubbub, is as credibly wan and bewildered as any backwater Louisiana home-schooler could be, though Stamm might have sprung for a special effect or two to help her along in her more devilish scenes. She contorts and gargles and can demonstrably slaughter house pets with the best of ’em, but it’s honestly a little hard to get all too worked up by a sophomore hanging out in a barn doing yoga in her jammies.

However, after all the substantial, anxious and effective setup, after introducing all these compelling people and egging us on to discover their relationships and wonder what the hell is really going on in that farmhouse, after 85 minutes in which every apparent explanation drops you through another trapdoor, Stamm, showing an ironic lack of faith in his material, just snaps on the lights with a big fat reveal that not only ruins the mood, but simply rips the stitches out of everything good the movie had going. Boom: cinemapocalypse.

Maybe at its core, the whole “devil inside” genre is predicated on a sociological, possibly theological, rubbernecking fascination with witnessing a good thing go bad. It may simply be a natural, albeit morbid, human instinct to be captivated by stories of naivety caving to knowledge, innocence to experience, youth to age—of paradises lost. But damn, Stamm, you ought to have realized that knowing the trick is the fastest way to killing the magic.

It makes one pine for a director’s cut that’s just two minutes shorter. After all the lofty, important and enduring questions his film flirts with along the way, only one lingers: what could possibly have possessed that guy?