In a side arm of the Spreewald Biosphere Reserve, Daniel Bartko's body, which is caught in a flap iron, is discovered in an empty barge. The opinion quickly prevails: Polish fur hunters were at work here. Criminal Commissioner Thorsten Krüger starts the investigation and learns that the Nutrias, a fur animal from South America, were introduced and bred to the Spreewald region in GDR times because of their coveted skins. Pathology proves that the percussion iron was only put on after Daniel Bartko's death. Daniel Bartko was married and Sorbe. His wife is pregnant. Daniel was a ferryman and to the annoyance of his traditional family not very attached to his Sorbian roots. Marriage to Tanja, a non-sorbine, daughter of the district forester, was an affront in the family's eyes.
Krüger falls in love with Tanja and assists her when Nutria skins are found in Daniel's shed. It turns out that Daniel did common cause with the fur animal hunters and that he wanted to leave his wife to share with his new love, the Polish Maria, to start a new life in Australia. After a deadly duel in the bog, Krüger convicts the real perpetrator.