Tabitha and her four best friends all wear Purity Rings, symbols of the virginity-until-marriage pledge they made as tweens. Now the girls are fifteen, and their rings have come to symbolize not only their purity, but also the friendships and identities they've built based on their shared faith. Simmering tensions rise to the surface and the group is split apart when one of Tab's friends admits that she and her long-term boyfriend have broken the pledge. In the midst of the confrontations, betrayals, confessions, and revenge that follow, each girl is forced to reexamine her friendships, her faith, and what exactly it means to be pure.