September AD 80. Flavia and her friends go to Rome to celebrate the Festival of Jupiter at Senator Cornix's town house. When a famous racehorse goes missing, Nubia sets out to recover it. The four friends find themselves caught up in a plot against one of the rival factions, the Greens. Who is trying to sabotage the charioteers? Could it be an inside job, or someone with a grudge from long ago? And how many men and horses will die before the killer is caught?