In the high summer of AD 77, laid-back detective Marcus Didius Falco is called upon to investigate the mysterious disappearance of a middle-aged couple who supplied statues to Falco's father, Geminus. The Claudii, nptorious freedmen who live rough in the pestilential Pontine Marshes, are the prime suspects. Falco, beset by personal problems, finds it a relief to consider someone else's misfortunes.

When a mutilated corpse turns up near Rome, Falco and his vigiles friend Petronius investigate, only for the Chief Spy, Anacrites, to snatch their case away from them just as they are making progress.As his rivalry with Falco escalates, it emerges that the violent Claudii have acquired corrupt protection at the highest level. Making further enquiries after they have been warned off can only be dangerous - but will this stop Falco and Petronius?

Egged on by the slippery bureaucrats who hate Anacrites, the dogged friends dig deeper while a psychotic killer keeps taking more victims, and the shocking truth creeps closer and closer to home...