Since the death of his wife, Klaus Baumann is just a shadow of his former self. His successes as a Berlin criminal inspector are a thing of the past, and his best friends are beer and schnapps. However, his boss still hopes for a turnaround and offers him one last chance: Chief Inspector in Hamburg. Trouble is inevitable for the big-mouthed Berliner, as no one understands him, except for Inspector Lena Arnold by his side. Baumann's first case drives him almost to madness. 21 letters arrive at the state criminal office, putting him and his team to the test. When more letters are found under a brutally mutilated corpse, Baumann nearly loses it. Who is sending him these letters and why?.