Münster. Professor Boerne's past catches up with him when a skeleton is found in a wooded area near the city.

A salt mine reveals the body of a security guard reported missing months earlier.

Cenk Batu is investigating undercover in the Hamburg Special Operations Command (SEK) on behalf of his superior Uwe Kohnau. Some officials there are suspected of working illegally as trainers abroad and selling their specialist knowledge. Batu manages to gain the trust of SEK man Lars Jansen, who is also said to be involved in the deal. The case seems almost solved when the SEK is suddenly called because of an alleged hostage situation.