The polluted waters of the canals in Venice are an ever-present issue; but environmental concerns become significant in Commissario Guido Brunetti's work when an investigator from the Carabiniere—looking into the illegal hauling of garbage—asks for a favor. But the investigator is not the only one with a special request. Brunetti's father-in-law needs help and a mysterious woman comes into the picture. And the Commissario soon finds himself in the middle of an investigation into murder and corruption more dangerous than anything he's seen before.