Anglo-Saxon women of royal blood sometimes became abbesses ruling great religious houses of both men and women. Some, like Hilda of Whitby, became among its greatest saints. But for others, the role, with its responsibilities and its privations, cannot have been easy to bear.

Thrust into the leadership of Whitby Abbey by a dynastic bargain, Mother Wynflaed, a king's daughter once engaged to a nobleman's son, attempts to live her responsibilities with grace both in the abbey and as councilor to her nephew, the young king of Northumbria. But though many call her mother, in her heart she burns with the desire for a daughter of her own.

When a beautiful young woman is found on the abbey doorstep, soaked and silent, Wynflaed feels as if she has birthed her out of the sea. She names her Agnes and offers her a mother's love. But Agnes shuns all affection and pulls down penances on her head for a sin she will not confess. As she unravels Agnes's terrible secret, Wynflaed must struggle with the unbearable question of whether Agnes is to stay or to go.