As Venice experiences a debilitating heatwave, Commissario Brunetti prepares to escape the city and spend time with his family in the mountains. For Ispettore Vianello, however, the weather is the last thing on his mind; it appears his aunt has become obsessed with horoscopes and has been withdrawing large amounts of money from the family business. Not knowing what to do, he consults Brunetti and asks permission to trail her. This 'unofficial' investigation leads them to the flat of Stefano Gorini. But who is this man? And why is Vianello's aunt giving him large amounts of money?

Meanwhile, Brunetti receives a visit from a friend who works at the Commune. It seems that discrepancies have been occurring at the Tribunale involving Judge Luisa Coltellini and Araldo Fontana, an usher with a flawless track record. Intrigued, Brunetti asks Signorina Elletra to find out what she can while he is away on his family holiday.
When news reaches Brunetti that Araldo Fontana has been murderedin a violent attack he returns to the city to head up the investigation. But why would someone want a good man dead, and what does he have to do with the discrepancies at the Tribunale? It soon becomes clear that things are not what they seem and as suspicions arise Brunetti has to dig ever deeper to uncover the truth behind the façade.