Betrayed by a servant, Tarzan and Maximus Praeclarus are captured and chained in the dungeons beneath the Colosseum of Castra Sanguinarius. Here he meets Cassius Hasta, the nephew of Validus Augustus. They fight as gladiators against man and beast and win in the end. Still the emperor does not grant them their freedom. With help of Appius Applosus, a friend of Maximus they escape and lead a revolution against Sublatus with help of the slaves from the nearby villages and the Waziri, brought by Nkima. Once Sublatus is defeated, Tarzan installs Dion Splendidus as Emperor and leaves for Castrum Mare to find Erich and support Cassius Hasta in ascending to the Throne.