Sister Fidelma sets off in A.D. 666 on a pilgrimage to the Holy Shrine of St. James in order to reflect on her commitment to the religious life and her relationship with the Saxon monk  Eadulf.  On the first night at sea, during a tempest, one of the pilgrims disappears, apparently washed overboard.  But the discovery of a blood-stained robe raises questions…Sister Fidelma, the Dark Age Miss Marple, focuses all her abilities on solving the mystery.