Roman Mysteries: The Charioteer of Delphi: Book 12

Flavia and her friends go to Rome to celebrate the Festival of Jupiter at Senator Cornix's town house, where they befriend the charioteer, Scopas, and find themselves embroiled in a campaign to sabotage one of the rival racing factions.
Who is trying to sabotage the chariot factions in the twelfth title in the Roman Mysteries series?
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?