In early summer in Franconia, unbearable humidity hangs over the land – and an unsettling suspicion begins to take root in Commissioner Behütuns: Did the Bamberg judiciary make a mistake years ago? Is a murderer possibly still at large? And does he perhaps only strike under these weather conditions? Why? And when again? Now? Behütuns delves deeper into the psyche of this perpetrator – or is he just a figment of imagination? Then a woman appears at the Nuremberg police station and makes a disturbing statement: She suspects that behind a series of tragic accidents lie murders, coldly planned and executed. Is this the idea of a twisted mind? The clues lead Behütuns' team years back and to southern Europe: to Corsica, Mallorca, and northern Italy, but also to various locations in Germany. And they find something that establishes an unexpected connection reaching far back to the Middle Ages.