As Venice experiences a debilitating heatwave, Commissario Brunetti prepares to escape the city and spend time with his family in the mountains. However, the weather is the last thing on Ispettore Vianello's mind; it seems 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 unofficially trail her, which leads to the flat of Stefano Gorini. But who is this man? And why is Vianello's aunt giving him large amounts of money?