Back in Rome after a dangerous mission to the Roman province of Baetica, Marcus Didius Falco is enjoying a drink of ill-travelled Spanish wine when he makes a gruesome discovery in the local fountain: a severed human hand.
Inevitably he is drawn into a search of the water supply and Rome's hundreds of miles of sewer and aqueduct. There he finds evidence of a whole series of murders. Each killing has taken place during a public festival, and the Roman Games are only days away. Time is running out if he is to prevent the murderer striking again.