Its heroine, Beckett (Sophie Curtis), has an inspired mystery to solve and all the secrets of a creepy-ritzy prep school to expose, but she's stubbed out for much of the film, victim of what appears to be the systemic drugging of the girls of Hamilton Prep by the gorgeous school nurse (Kelly Reilly). Tending to uniformed schoolgirls, she always looks as if she just left the Vanity Fair Oscar party — and as if she's trying to keep her smile going even though she's bitten into something sour. She's horning in on Beckett's widowed father, but she plays nice as long as Beckett doesn't poke into her affairs. As Beckett is beset by ghosts and has found evidence of three suspicious suicides at Hamilton, it's a marvel they get along as long as they do. But just when it seems Beckett's about to crack the case, the plodding Innocence sends her to Central Park for slo-mo skateboard lessons.
Things go nuts, eventually, with revelations of — well, look, the clues are the size and complexity of Duplo blocks, so I'm going to spill: The women who run Hamilton look young and fab because they sup upon the blood of virgins. The school's staff encourages kids toward "purity" — although the movie's never brave enough to satirize abstinence-only sex ed. But it is courageous enough to let its teen heroine unburden herself of her virginity at the time of her choosing with a partner she picks.