Abandoned at St Mary's Boarding School for Girls, Heather thought life couldn't get much worse. She was wrong. Waiting for her is the malevolent Sister Merce. As the danger to Heather increases, hope arrives with Amy, a spirited girl whose physic abilities reveal a mystery involving two long-dead 'fallen' girls, Jennifer and Rachel. Using a diary and an amulet, and assisted by the sweet-hearted Patrick and self-destructive Caleb, the four girls are drawn into a liminal space where they must stand together and use the power within themselves to destroy the Sisterhood.