In his many years as a Commissario, Guido Brunetti has seen all manner of crime and known intuitively how to navigate the various pathways in his native Venice to discover the person responsible. Now, in the thirtieth novel in Donna Leon's masterful series, he faces a heinous crime committed outside his jurisdiction. He is drawn in innocently enough: two young American women have been badly injured in a boating accident, joy riding in the Laguna with two young Italians. However, Brunetti's curiosity is aroused by the behaviour of the young men, who abandoned the victims after taking them to the hospital. If the injuries were the result of an accident, why did they want to avoid association with it?

As Brunetti and his colleague, Claudia Griffoni, investigate the incident, 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 what proves to be a gut-wrenching case, Brunetti needs to enlist the help of both the Carabinieri and the Guardia di Costiera. Determining how much trust he and Griffoni can put in these unfamiliar colleagues adds to the difficulty of solving a peculiarly horrible crime whose perpetrators are technologically brilliant and ruthlessly organised.