Book clubs and virginity can be bad for a girl’s health.

At least that’s the case in “Innocence,” a messy if sporadically entertaining horror thriller based on a well-received novel by Jane Mendelsohn.

Adapted for the screen with an eye toward a young-adult audience, “Innocence” stumbles over unexplained Gothic tropes, poor pacing and a strange sense that the story’s villains are too remote from the main action.

On the plus side, there’s an appealing cast anchored by the terrific British actress Kelly Reilly (“Mrs. Henderson Presents”) as Pamela, a school nurse with a silky, feline demeanor that can lull anyone toward destruction.

    Most Read Stories

“Innocence” begins with a death that leaves Beckett (Sophie Curtis), a shy teenager, without a mother, and inexplicably leads the girl’s dad (Linus Roache) to enroll her in a Manhattan preparatory school for young ladies.

Staffed and supported by a crowd of beautiful, youthful women who frequently gather behind closed doors for alleged book-club meetings, the school holds shadowy secrets about the fatalities of virgin students.

The dead appear to Beckett as whispered voices and apparitions, though why or how that is relevant to her story is a mystery.

Despite gaps in logic, “Innocence” has enough marginal weirdness (the personality changes in one boy spellbound by a curiously powerful diva-student are fascinating) to keep it afloat.

Still, co-screenwriter and director Hilary Brougher loses impact through long, dewy scenes of young romance between Beckett and a confidante (Graham Phillips). Even the most starry-eyed kid watching “Innocence” will want this movie to get back on track.

Tom Keogh: tomwkeogh@yahoo.com