When two young American women are badly injured in a boating accident, joy riding in Venice's Laguna with two young Italians, Commissario Guido Brunetti's curiosity is aroused by the behaviour of the young men, who abandoned the victims after taking them to the hospital. As Brunetti and his colleague, Claudia Griffoni, investigate, they discover that one of the young men works for a man rumoured to be involved in more sinister night-time activities in the Laguna. To get to the bottom of the mystery, Brunetti needs to enlist the help of both the Carabinieri and the Guardia Costiera.

Determining how much trust he and Griffoni can put in these unfamiliar colleagues only adds to the difficulty of solving this peculiarly horrible crime. Donna Leon's landmark thirtieth Brunetti novel is as powerful as any she has written, testing Brunetti to his limits, forcing him to listen very carefully for the truth.