Empress Centuria has ordered her Lizardmen to hunt and kill Tribune, who flees to the treehouse for help. They track him there and overwhelm our heroes. Malone, Marguerite and Roxton are taken prisoner along with Tribune and brought back to Centuria's city. Malone, posing as Professor Challenger, is ordered to make gunpowder, while Roxton and Tribune are sent to the gladiators' dungeon.