As the nuns of St. Frideswide's priory prepare for the welcome end of Lent, their peaceful expectations are overset by the sudden return of long-vanished Sister Cecely. Nine years ago she fled from the nunnery with a man. Now her lover is dead and she has come back, bringing her illegitimate son with her.

She claims she is penitent, that she wants only to redeem her sin and find safe haven for the child. Neither she nor her son can be turned away, but their presence begins to stir doubts and questions in the hearts of some of the nuns about their own faithfulness to this enclosed life they've chosen to live.

Sister Cecely may be penitent-however much Frevisse may doubt it-but fully truthful she is not, and as the apostate nun's lies begin to overtake her, dangers of more than one kind-and maybe murder-become an unwanted part of life in the priory.