When Sister Fidelma sets out on a pilgrimage in the autumn of AD 666, her main preoccupation is to reflect on her commitment to the religious life and her relationship with the Saxon monk, Eadulf, whom she has left behind. Complications arise during the first night on the ship when one of the pilgrims is apparently washed overboard.

The discovery of a blood-stained robe raises the question of murder and Fidelma finds herself having to focus all her abilities on solving the mystery. Death dogs the tiny band of pilgrims in the close confines of the ship, but is not until the Holy Shrine is almost reached that the amazing truth is uncovered...