In the late autumn of A.D. 666, Sister Fidelma, an advocate of the Brehon law courts, embarks on a pilgrimage to contemplate her commitment to Ireland's Celtic Church and her relationship to the Saxon monk Eadulf. On a ship bound for the Shrine of St. James in Iberia, she encounters Cian, her first love, who deserted her ten years ago -- and whose sudden presence reminds her of a past she'd rather forget.

Before Fidelma can come to terms with seeing Cian again, a fellow traveler disappears, apparently washed overboard by rough weather. But the appearance of a bloodstained robe leads Fidelma to wonder whether a murderer has accompanied her on the voyage...