A fisherman finds a dead body in the mudflats. At the same time, a newspaper receives samples of biological warfare agents from blackmailers. Inspector Ann Kathrin Klaasen is called to investigate their threat to poison East Frisia’s water supply. Lab tests confirm the authenticity of the samples, and no one realizes yet that the two cases are connected. Ann Kathrin’s sights fall on her former boss, Ubbo Heide. What secrets is he harboring?