Roxton is looking for the materials for a crossbow to bag a T-Rex, but when one actually interupts him in his labors, he runs in the direction opposite his fellow travelers to keep them safe. He winds up falling into a hole that suddenly opens up. When the rest of the group search for him, they also fall into the hole, which turns out to be a whirlpool. It sucks them all under the water, and they emerge in a lake. They quickly find out that in this part of the plateau, the dominant species are lizard-like men, descendents of dinosaurs, and the humans are subservient to them. There is an ancient Roman structure to this civilization, including gladiator-type battles. While Marguerite and Veronica are forced to change into silky gowns for the entertainment of Tribune, the lizard-people's leader, Roxton is chosen to fight another human prisoner. The slaves and travelers rebel, and overthrow the lizard-men's intolerable rule, but not without loss ~ Roxton's opponent's sister ~ a rebel leade

The explorers are caught in the middle of a war between Tribue, with gunpowder in toe, and Drakul and his barbaric raiders. One of them will be lost, possibly forever, when this battle reaches its cliffhanger!

On a bridge spanning a deep gorge, a fierce battle unfolds with Drakul's raiders. Marguerite and Veronica watch as Summerlee is hit. Tribune, betrayed by Drakul, hurls a bomb that destroys the bridge...throwing the men into the river far below. Veronica clings to the hope that her friends have survived and searches for them with Marguerite. Once reunited, they discover that Tribune has saved Roxton's life and demands a favor in return. Since they need a boat to return home, they follow Tribune to a run-down fishing village - where he disappears. A beautiful prostitute named Raina informs them that Nemak has enslaved the town. When our gang clashes with Nemak and his goons, they are thrown into jail.

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.

During a powerful thunderstorm on the plateau, all five of our heroes experience dreams and visions of their ""lost"" colleague, Summerlee, who had disappeared into a raging waterfall and presumed dead. Malone sets off after this ghost, and Challenger Marguerite and Roxton follow Ned. The three are ambushed by cannibals who fancy Marguerite's arm for an aperitif. Roxton and Challenger break free and save her, and then the three resume their hunt for Malone, only to be trapped by a hungry T-Rex.

Ned meanwhile, has fallen and knocked himself out. He regains consciousness, concussed and thirsty, and follows Summerlee's ghost along a dry riverbed. He stumbles and twists his ankle, but still hobbles on. Summerlee appears to be leading him to the now dry waterfall where he was last seen.