It’s 1944 and World War II rages on as the nuns of isolated Scottish monastery St. Augustine’s prepare for an incoming storm front. During the night a baby in a basket is left on the doorstep and the sisters take it in to care for it. However Sister Agnes soon suspects the child is the son of the Devil and she is locked up by the nuns for her own safety. Has the isolation driven her mad or is their weight in her suspicion?