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, born a king's daughter and once engaged to a nobleman's son, accepts her responsibilities and attempts to live them with grace. 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. But Agnes shuns all affection and pulls down penances on her head for a sin she will not confess. As she slowly unravels Agnes's terrible secret, Wynflaed must struggle with the unbearable question of whether Agnes is to stay or to go.