Private detective Peter Mang is found half-naked in a construction pit with a dog tattoo on his neck and puncture wounds in his back. Has he become the victim of his secret investigation? The trail leads Inspector Thiel to the villa of the industrialist family Rummel. Despite the clean facade, Sabine and Markus Rummel's marriage obviously seems to be crumbling: after all, the photos taken by the detective show that the factory boss and his new assistant Christine Schauer have more in common than just an employment relationship. Meanwhile, Prof. Boerne is once again investigating on his own. The fact that the murdered private detective looked so similar to him is something that doesn't bother the forensic doctor. The dead man's striking tattoo leads him to a relevant tattoo studio in Münster. Here he meets the Belarusian Jan Sievic – and his fighting dog.

Borowski goes undercover, placing a personal ad to bait a killer who seems to find victims through a lonely hearts site.

A gruesome sexual murder shocks Münster. The victim, a young law student, was found strangled in her apartment. “Do we all have to be afraid now?” is the headline in the local press. But there is not much to suggest that a serial killer was actually at work here. However, the victim's ex-boyfriend André Pütz, a freelance photographer who mainly travels to crisis areas around the world, is an urgent suspect. Recently he had repeatedly stalked the young woman. When Inspector Thiel and Prof. Boerne surprise him at home, he flees headlong. And yet Thiel resists drawing hasty conclusions. He discovers parallels between the crime and other cases. Above all, the extremely attractive bank employee Anna Schäfer, whose apartment was recently broken into, won't let him go. But at first he meets her very aloofly.

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