Detective Guido Brunetti is tasked with finding out which of his colleagues is involved in the leak of information from the police station. Almost at the same time, an acquaintance, Signora Crocera, asks the detective to help her: her son has started taking drugs. Soon her husband Tullio is found under a bridge with a serious head injury. Brunetti begins to look for a possible connection between this incident and the boy's behavior. The detective is hampered by a “mole” lurking in the precinct. Wandering in a labyrinth of contradictory assumptions, Brunetti follows into the world of criminal deals and fraudulent scams.