In the greenish waters of Maschsee, a corpse floats. The tongue of the deceased lies severed in the Stöckener cemetery in Hanover, on the gravestone of the victims of the mass murderer Fritz Haarmann. The Hanover criminal police quickly discover that the murdered man is a prominent psychiatrist, an expert on sex offenders, whose cool, rational theories have even caused a stir on television. But who wanted to silence this man so symbolically?.