Libertus, freedman and pavement-maker, finds himself in Londinium at the invitation of the Roman Governor when news arrives of the brutal murder of Caius Monnius, the chief corn-officer. Libertus is asked to investigate but his enquiries lead him in disparate directions. Who is the guilty one? The keeper of the granaries? The sinister Calyx and Glaucus, managers of the best chariot-racing team? Or Fortunatus, the handsome charioteer whose relations with the dead man's wife were reputed to be less than honourable? Not until Libertus finds a second corpse does he begin to understand what lies behind the corruption surrounding the interests of Monnius and the chariots of Calyx.