Barbara Hansen is the first to notice it in disgust: the bone her singing teacher Schilling's standard poodle is chewing on. After Hubert takes a closer look, it becomes clear that it is a human femur.

The detectives and their boss, Sabine Kaiser, must assume that an entire skeleton lies at the site where the male bone was found. With the help of the dog, they begin searching and, after a few detours, are led to a grave at the Wolfratshausen cemetery. But no man is buried in that grave—and the discovered skeleton also shows signs of an accident. Now they must solve a crime that dates back 15 years.

But where should they begin their investigation? With the official owners of the grave plot, with the woman who fainted at the sight of the skeleton in the cemetery, or with the dog's owners?

There are plenty of possible leads, and at times Hubert is annoyed by the feeling that he has to pursue them all on his own. His colleagues Riedl, Bayer, and Girwidz have secretly been given a special assignment by Sabine Kaiser: to make Hubert's 35th service anniversary a very special day. The fact that the three of them are taking singing lessons from the dog's owner—so they can serenade their colleague—may unexpectedly prove helpful in solving the crime.