In 1928, Emily Locke's final year at the isolated Briarley School for Girls is derailed when Violet, the school's brightest star (and a cunning beauty for whom Emily would do anything), falls to her death on her eighteenth birthday. Emily and her buttoned-up rival Evelyn are, for once, in agreement: Violet's death was no accident. There's an obvious culprit, the French schoolmistress with whom Violet was getting a little too close - they just need to prove it.

Desperate for answers, Emily and her classmates turn to spiritualism, hoping for a glimpse of wisdom from the great beyond. To their shock, Violet's spirit appears, choosing pious Evelyn as her unlikely medium. And Violet has a warning for them: the danger has just begun.