In December of 666 A.D., Fidelma of Cashel and her companion Brother Eadulf, having completed their business with the Archbishop of Canterbury, make one final journey before returning to Ireland. At the insistence of Brother Botulf, a childhood friend of Eadulf, they detour from their trip to Eadulf's home village and make their way to Aldred's Abbey. Arriving at midnight on the night of the old pagan festival of Yule, as requested, they find Botulf's dead body - his head caved in by a blunt instrument.
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.