In January of 668 A.D., Fidelma of Cashelโsister to the king of Muman, an advocate of the Brehon law courts and a religieuse in the Celtic Churchโis called to investigate the brutal murder of Abbess Faife and the mysterious disappearance of six young female religieuse accompanying her on a short pilgrimage away from her abbey. When Sister Fidelma and her husband, Brother Eadulf, arrive they find that there has been another death under mysterious circumstances, one of the senior scholars of the abbey has been bludgeoned. These two seemingly unrelated deathsโand the further mysteries of the trade ship lured to its doom on the rocky western shore of Ireland and the rumored figure of "The Master of Souls" wrecking havoc and raising rebellionโcombine to create one of the most perplexing mysteries ever faced by the redoubtable Fidelma.