Emperor Caligula's favourite racehorse, Incitatus the Swift, eats gold for breakfast, attends the Senate and has 18 slaves to look after him. When Caligula names Incitatus heir to the throne, the horse's stylist Livia and young charioteer Marcus are caught up in a plot to assassinate the crazy emperor and restore the Republic to Rome. Livia is sentenced to death fighting tigers, while Marcus must risk life and limb racing in the Circus Maximus...