The findings of forensic doctor Prof. Karl-Friedrich Boerne were an open skull fracture. A man's body is discovered near Lake Aasee. The first indication for Commissioner Frank Thiel are tire tracks in the mud. But instead of finding the perpetrator, this clue leads the investigator duo Thiel and Boerne to the identity of the victim.

The murdered Wolfram Baermann was an engineer and had successfully entered the wind turbine business with his long-time friend Klaus Weisberg. The young widow Rike Baermann, a physiotherapist, describes her husband as an extremely reserved person who sometimes withdrew for days. Wolfram Baermann suffered from depression since his childhood.