Sister Fidelma and her companion Brother Eadulf are on their way to visit the new Archbishop of Canterbury, when their ship is blown off course and they land on the coast of the Welsh kingdom of Dyfed.

They are given hospitality by King Gwlyddien and Abbot Tryffin of the Abbey of Dewi Sant, and are asked if they would help to solve the mystery of how the entire monastic community of the Abbey, including the King's eldest son, could vanish into thin air. It's not long before the trail leads to deaths and treachery in high places and Fidelma and Eadulf are faced with a sinister and baffling puzzle.