Circus Maximus: Rider of the Storm

Dido gallops headlong into her third adventure, following her escapades in the riveting and action-packed Race to the Death and Rivals on the Track.
Dido is reconciled to leaving the racing track and staying at home to train horses with Scorpus and Parmenion. But a storm is brewing. It brings with it a fiery black stallion, uncannily like Dido's beloved Porcellus.
Word arrives from Rome that her cousin, Abibaal, a talented young charioteer, has been recruited to compete for the evil emperor, Caligula. To save Abibaal, Dido must return to the great Circus Maximus track where she once drove to glory herself, confront her enemy Caligula, and face the toughest, most dangerous race of her life. For 9+.
'Rich in period detail, with a few real historical characters - its principal invention the idea that a woman might have been a charioteer - this is an involving, well characterised tale that feels original'
Sunday Times, Children's Book of the Week, on Race to the Death