The third case for Halle detectives Koitzsch and Lehmann begins with a mysterious death in the bathtub. It quickly becomes clear that elderly Mrs. Krüger did not die of natural causes, but was murdered. The overzealous building superintendent comes under suspicion of having something to do with the crime. Clues lead the two investigators back into the past, to the unsolved murder of Uwe Baude and other unexplained cases. A grim suspicion arises that they are dealing with a serial killer. In the process, they encounter an old acquaintance — Mrs. Sommer. Could she be the key to solving the case? But before the two detectives can find the killer, Koitzsch himself finds himself in mortal danger.