When the Abbess Etain, a leading speaker for the Celtic church, is found murdered, suspicion falls upon the Roman faction. In order to diffuse the tensions that threaten to erupt into civil war, Oswy turns to Sister Fidelma of the Celtic Church (Irish and an advocate for the Brehon Court) and Brother Eadulf of the Roman church (from east Anglia and of a family of hereditary magistrates) to find the killer. But as further murders occur and a treasonous plot against Oswy matures, Fidelma and Eadulf soon find themselves running out of time.
Once safely ashore, Fidelma—sister to the King of Muman and an advocate of the Brehon law courts—is determined to bring the killers to justice, not only because her training demands it but also because one of the victims was her cousin. The only clue to the killer's identity is the symbol of the dove on the attacking ship's sails, a clue that leads her on a dangerous quest to confront the man known as The Dove of Death.
As Fidelma and Eadulf soon learn, however, murder isn't the only danger which faces those in the abbey. The ghost of a young woman haunts the cloister shadows, a ghost which closely resembles the Abbot's dead wife. Now it will require all of Fidelma's skill as an advocate of the Brehon Courts to unravel the mystery and uncover the truth behind these events before those secrets take yet another life.