Open skull fracture is the finding of forensic pathologist Prof. Karl-Friedrich Boerne (Jan Josef Liefers). A man's body is discovered near Lake Aasee. The first indication for Commissioner Frank Thiel (Axel Prahl) 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 successfully entered the windmill business with his longtime friend Klaus Weisberg (Harald Schrott). The young widow Rike Baermann (Julika Jenkins), a physiotherapist, describes her husband as an extremely withdrawn person who sometimes withdrew for days. Wolfram Baermann has suffered from depression since childhood .
When the forensics team comes across smudged remains of blood in the Baermanns' bedroom, it becomes clear that Wolfram Baermann was killed in his own bed. His wife is increasingly under suspicion. Somehow the Baermann family seems to have been struck by fate. A few days earlier, his father's second wife, Henner Baermann (Otto Mellies), died in the bathtub. And the sister Hanne (Jenny Schily) lives in a psychiatric clinic because she has obviously suffered from trauma since childhood. Prof. Boerne's detective curiosity is aroused, maybe Hanne is the key to the murder case.