July, 1921: England is suffering a heatwave and the coast of Northumberland, just across the border from Scotland, is filled with holiday-makers bird watching and enjoying the beaches. Pilgrims also come to visit the home of Saints Cuthbert and Aiden—the founders of Christianity in England—located on the "Holy Island" of Lindisfarne, accessible by a causeway at low tide.

When the murdered body of a local man washes ashore just south of Lindisfarne, the government and the Church of England are concerned about protecting both the reputation of the Church and the sacred sites that are a destination for hundreds of pilgrims at this time of year. With his ability to move in the highest social and political circles, Rutledge is sent by Scotland Yard to solve this crime and dispel any association with the Church.

Facing a puzzling case and a cast of locals that don't take kindly to outsiders, the newly promoted Rutledge meets one of the most challenging cases of his career. To solve it, he'll also have to confront his own demons left over from his time in the war.