Breslau, 1919. The hideously battered bodies of four young sailors are discovered on an island in the River Oder. When Inspector Mock arrives at the scene to investigate, he discovers a note addressed to him, asking him to confess his sins and to become a believer. As he endeavours to piece together the elements of this brutal crime, Mock combs brothels and drinking dens of Breslau and is drawn into an insidious game by the murderer; ultimately he uncovers a secret society which appears to have the Inspector himself in its sights.