Historical drama. A ship docks at Ostia carrying a team of gladiators, booked to entertain at a private function. Nubia thinks she may have glimpsed her missing brother amongst them, but as the children go to the arena, they discover a mystery that endangers the life of the Emperor's brother, Domitian. Jonathan must face the most frightening of the gladiators and Flavia and Nubia need all their courage to deal with a ravenous beast.