One year after the events of \"Kickboxer: Vengeance\", Kurt Sloan has vowed never to return to Thailand. However, while gearing up for a MMA title shot, he finds himself sedated and forced back into Thailand, this time in prison. He is there because the ones responsible want him to face a 6\'8\" 400 lbs. beast named Mongkut and in return for the fight, Kurt will get two million dollars and his freedom back. Kurt at first refuses, in which a bounty is placed on his head as a way to force him to face Mongkut. Kurt soon learns he will have no other choice and will undergo his most rigorous training yet under some unexpected mentors in order to face Mongkut in hopes to regain his freedom.
The story picks up at the point where "The Robe" ends, following the martyrdom of Diana and Marcellus. Christ's robe is conveyed to Peter for safe-keeping, but the emperor Caligula wants it back to benefit from its powers. Marcellus' former slave Demetrius seeks to prevent this, and catches the eye of Messalina, wife to Caligula's uncle Claudius. Messalina tempts Demetrius, he winds up fighting in the arena, and wavers in his faith.