One could refer to “Innocence” as a pint-sized version of “Rosemary’s Baby,” but that would be unfair to everybody involved—with Polanski’s 1968 masterpiece, that is. Based on a 2001 novel by Jane Mendelsohn, it involves virginity rather than pregnancy, but the larger context of conspiratorial witchcraft is similar.

The protagonist is Beckett Warner (Sophie Curtis), a teen who moves with her novelist father Miles (Linus Roache) to New York City after her mother’s death. Beckett enrolls at Hamilton, a prestigious girls’ prep school, but soon finds the place unsettling. It’s not just that the teachers—a bunch of svelte, voluptuous types—stroll around as though they were in a different profession altogether—the oldest one. It’s also that her fellow students—with one exception, Jen (Sarah Sutherland)—are a mostly standoffish, snooty bunch, some of whom seem curiously close to the staff.

The fact that Beckett suffers from nightmares also figures into her unease. Some center on her mother, but others feature apparitions that appear to refer to the school’s past: her investigations suggest a troubling history of suicide among the girls, and when a current student (Chloe Levine) leaps to her death from the school’s ledge right in front of Beckett and Miles, it’s further evidence of the place’s bad vibe. Beckett regularly consults a therapist (Sarita Choudhury), but she offers little assistance. And as if all that weren’t enough, Miles is soon seduced by the school nurse Pamela Hamilton (Kelly Reilly), who becomes virtually a fixture in the Warner apartment.

A series of oddities—cups whose content originally seems to be red but suddenly becomes tea, old photos that show women suspiciously like the current staff—as well as a bit of research into the institution’s history and the occult eventually persuade Beckett that the staff is actually a coven of witches that have maintained their youthful appearance by drinking the blood of virgins—and that she’s next on their list of sacrificial victims.

Fortunately Beckett has a remedy ready to hand, so to speak, in the person of Tobey Crawford (Graham Phillips), a cute boy from another school whose mother Natalie (Stephanie March) is the friend of Miles who arranged for their apartment (and apparently for Beckett’s acceptance at Hamilton). The kids meet cute (she literally bumps into him), but they hit it off, and soon he’s teaching her to skateboard, as well as other things that, as the thoroughly unsurprising denouement demonstrates, have a momentous effect on the blood she can supply. That ending is a pretty confusing affair, involving an exchange of phones, some confusion on Tobey’s part, the disappearance of Jen, the appearance of some sort of wraith, a sacrificial ceremony in the school garden that looks like something lifted from Druidic ritual, the stabbing deaths of a couple of characters, and a fire. But it all turns out okay, apart from a demonic gleam in Beckett’s eye as the curtain comes down.

It’s pretty much a certainty, though, that this final twist will not result in a sequel, unless it’s of the direct-to-DVD variety. “Innocence” is an extremely silly attempt at a young adult thriller that winds up laughable rather than scary. Perhaps it’s meant to carry some metaphorical weight as a feminist coming-of-age tale, but if so director Hilary Brougher, who also co-wrote the adaptation with Tristine Skyler, doesn’t possess the ability to get that across; in fact, she can’t even shape the material into an effective piece of pulp. Nor does she get acceptable performances from her actors. Curtis is curiously drab, and though Phillips flashes a nice smile, that’s about the extent of what he has to offer. But while they and the other youngsters in the cast are nothing special, the really bad performances come from the adults. Playing a milquetoast, the usually reliable Roache comes off as a bland nonentity, and Choudhury barely gets past a mere recitation of her lines. Worst of all, however, is Reilly, who slinks around trying to look seductive and ends up like a parody. It’s a performance that’s the purest camp, and theoretically one can enjoy all her vamping as a guilty pleasure. But if she’s sending the material up, why is everyone around her playing it in deadly earnest?

On the technical side, the picture is innocent of anything distinctive. The production looks a bit on the chintzy side, though the locations are attractive enough, and David Rush Morrison’s cinematography is decent, though the bluish visual effects in Beckett’s visions are mediocre. The score by tomandandy is unmemorable.

It’s possible that Mendelsohn’s novel, which was reasonably well received, had some virtues. But whatever they might have been, they’re not evident in this inept adaptation.