When the body of an wealthy elderly woman is found, brutally murdered in her Venetian flat, it is soon clear to the police that the prime suspect is her Rumanian maid, who has disappeared and is heading for Rumania. When the woman is approached by the border police as her train is leaving Italy, she makes a run for it and is killed as she crosses the tracks in front of an oncoming train. She has a considerable sum of money on her and her papers are obvious forgeries. Case closed.
But when the old woman's neighbour returns from a business trip in London, it becomes clear that the maid could not have had time to kill the old woman before catching her train, and that the money on her was not stolen. Commissario Brunetti decides - unofficially - to take the case on himself.
As Brunetti learns more of the old woman's family, it becomes clear that this is probably not a crime motivated by greed, rather that the probable motive connects with the temptations of lust. But perhaps Brunetti is following a false trail and thinking of the wrong deadly sin altogether . . .