The body of a teenager, fourteen-year-old Anatoly, is found in the ditch of the monkey barn at the Heidelberg Zoo. The case seems clear: a boy crawled through a hole in the fence at night and became the victim of an aggressive male gorilla, frightened by the invasion of his territory. However, Hauptcommissar Theuer, trusting his instincts, is in no hurry to close the case, although he has nothing but vague suspicions. Some time later, another corpse is discovered in the monkey house - a gypsy youth. If witnesses are not found, Theuer will have to interrogate a gorilla for the first time in the history of jurisprudence.