Six 15 year-old girls are boarders in a sinister school where they spend every single day terrorised and maltreated by a fearsome nun. One day the nun discovers that one of the girls is pregnant. Scandalised by this turn of events, she tries to purify her. The girls watch as their friend is tortured and decide to help her. The nun was never seen again and the school suddenly closed a few weeks afterwards. Seventeen years later, each of the six girls has built their individual lives. They have lived hoping they would become distanced from this terrible secret. But when two of the girls are brutally murdered, they realise that the nun is back. They return to the school to deal with their past.