In 1940s, the nuns of a remote Scottish island convent ready for an impending storm, but when a baby is left on their doorstep, Sister Agnes becomes convinced he is the Devil and wants to kill the child. After Agnes is locked away a grim series of events ensue as the storm rages, and as her Sisters begin to question faith and reality, Sister Eleanor must try to repent and survive the dark events at St Augustine’s.

An abrasive caregiver and a stubborn elderly woman must reconcile their contrasting personalities to find inner healing.