Breathe

In Breathe, a 17-year-old French high schooler named Charlie (Josephine Japy) is a good student and a virgin when she befriends Sarah (Lou de Laage), a self-confident new girl at school whose mother is doing good works in Africa while Sarah lives with an aunt. That is the story Sarah tells, but as her behavior becomes meaner and more erratic, Charlie discovers a sadder truth. The girls become close, and soon the sexually precocious, drinking, smoking Sarah turns against Charlie. She bullies and humiliates the devastated Charlie, who is too hurt to confide in her mother, her friends, the school, or anyone about the cruelty and lies coming from the duplicitous Sarah. When Charlie learns that Sarah, in fact, lives with her mother, an impoverished and violent alcoholic, Charlie forgives Sarah and swears to keep the secret. Sarah, proving herself a sociopath, doesn't accept the forgiveness and mercy but instead attacks again, turning it all around on poor, naïve Charlie. The result is (spoiler alert) a fatal disaster.