The Catholic Church combats a global rise in demonic possessions by opening a school to train priests in the Rite of Exorcism. On this spiritual battlefield, an unlikely warrior rises: a young nun, Sister Ann. Although nuns are forbidden to perform exorcisms, a professor recognizes Sister Ann's gifts and agrees to train her. Thrust onto the spiritual frontline with fellow student Father Dante, Sister Ann finds herself in a battle for the soul of a young girl (who Sister Ann believes is possessed by the same demon that tormented her own mother years ago), and soon realizes the Devil has her right where he wants her... and it wants in.