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.

While looking for a way off the plateau, Roxton, Malone, and Challenger are saved by three Amazon women from an attack by a vicious flock of pterodactyls. Invited back to their camp, they find there are no men or boys, yet they are welcomed with open arms. While the Amazons celebrate by the light of a full moon, the men happily learn that it's breeding time -- and they have been chosen as studs. By the time they realize they will die as soon as they have served their purpose, it's too late to save themselves.

Challenger is trying to harness the energy of lightning when a gigantic bolt splits the sky. In a blinding flash, the ground is scorched, and by some miracle, no one is injured. In the silence after the thunder, the sputtering sound of a small engine is heard, and a small plane appears in the distant sky. It drops from view, crashing into the jungle. All survive: four modern day tourists - a couple, a middle-aged man and a gorgeous young woman. The group are set upon by a hostile tribe and taken prisoner. Our explorers arrive to find only the disabled plane, which Challenger and Malone set about trying to repair. Kenner, the leader of the hostile tribe, is fascinated by his captives but keeps them in a dungeon. Roxton and Veronica devise a plan to save them.

While mapping an unexplored valley, Roxton is surprised by a terrified young woman, who after uttering an enigmatic warning, dies in Marguerite's arms. Roxton, Marguerite, and Malone head toward an ominous castle when a sudden rainstorm forces them to seek shelter. There, under a mysterious influence, the three are led to separate rooms where they each find opulent evening wear of the same vintage as that worn by the young woman. Marguerite and the two men begin to take on new personalities, eerily re-enacting a romantic triangle of intrigue, with Marguerite playing Roxton against Malone as both men compete for her attention. Meanwhile Challenger and Veronica similarly find themselves at the castle, where they are welcomed by Roxton, Marguerite, and Malone, all strangely possessed by the spirit-wearers.

A riderless horse approaches our explorers, as if on a mission. When Roxton saddles up, the horse carries him to a mountain tribe, who welcome him as their king. Roxton tries to decline, but when the royal advisor, Balar, tells him that if he's an imposter; he shall die, Roxton reconsiders. Using the horse, Roxton tries to warn his friends. Balar has the horse followed and they are captured. One of the customs of the tribe is to sacrifice a virgin to appease a monstrous dragon, but Roxton saves the young woman and steps right into Balar's trap. The only way to stop the dragon now is for the rightful king to hunt it down and kill it.

When Marguerite starts being nice to everyone, they wonder what she's up to. Even when pushed to find out why she's acting this way, she maintains her uncharacteristic serenity. In the jungle, Roxton and Veronica are attacked by a dinosaur that after giving them a huge scare, starts to move very clumsily, giving them a chance to escape. We learn that an alien invader, who could not control the dinosaur's huge body, occupied it. We also learn that Marguerite's body has been possessed when she drops her spoon into a vat of boiling water and plunges her arm in to retrieve it - with no ill effect. We discover that the Alien Invaders are skeletons that our heroes have to fight.

Our adventurers recover an ancient map showing the escape route from the Lost World. Knowing they will face skeptics in the scientific world to which they shall return, Challenger and Malone capture a T-Rex egg to take with them. Veronica cannot share their joy, however, for she must continue her search for her long lost parents. Malone's dreams of successfully returning to his beautiful fiancée in London appear to come true. But is this what he really wants?

A mysterious old woman, a shape-shifter, appears to Veronica, convincing her that her lost parents are safe in El Dorado. The woman gives her the directions to its entrance in a rock wall, and warns that she must tell no one and can never return. When Veronica unwittingly releases a savage giant from captivity, Marguerite and the others must use all their talents to subdue him again.

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.

The Lost World is in the grip of a crippling drought. Our adventurers are saved from a pack of thirsty Raptors by a magnificent young woman who begs them to escort her to her pueblo. She confesses that she is a survivor of the original colony, which had discovered the Fountain of Youth. Her supply is diminishing, however, and she must return to the Fountain cave--or die. Marguerite, with visions of eternal youth and wealth, leads the others after Ana.

The Lost World is shattered by gunfire as trophy hunters try to capture a Troglodyte child. Veronica swings through the jungle to save him, and becomes the hunters' new target. She escapes to the Treehouse to warn her friends just ahead of the hunters. One of the hunters declares that he has been commissioned to locate the Challenger expedition and help them return to England. Despite Veronica's warnings, and Marguerite's suspicions, the hunters are welcomed and set up camp nearby.

As mysterious drums sound through the jungle, Roxton is stalked and seduced by a beautiful woman, Danielle, who tells a harrowing tale of Trogs attacking and taking over her village. Seeking refuge at the Treehouse, she manages to charm the men but arouses the women's suspicions. Their mistrust is justified when Danielle makes a voodoo doll in Roxton's image and lures him back to her village, where it turns out, she is the one who controls the Trogs and an army of zombies. When the others discover that Roxton has been enslaved, they quickly devise a plan to infiltrate the village and rescue him.

Challenger is knocked unconscious by a falling pig trap while searching for medicinal herbs. The three young hunters who set the trap drag him back to their hidden village. Veronica and Marguerite follow the hunters' tracks and make their way past the jungle defense into the village, populated by a group of young orphans. They learn that the village is protected by an enormous plant that emits a deadly gas when disturbed and must be fed fresh meat daily. While the trio attempt to find a way out of the village, the tribe seizes Challenger and pushes him toward the plant's jaws. Will Challenger be the plant's next meal?

The explorers have a strange guest at the Treehouse who impresses Challenger with his knowledge of geology. Meanwhile something attacks Challenger's electrostatic accumulator. The explorers chase after a group of underground dwellers whom they believe to be the culprits. Their guest turns out to be one of them, and the explorers are soon taken hostage. It turns out that the underground dwellers need Challenger's scientific expertise to help them evolve above ground.

Roxton and Marguerite are out looking for a way off the plateau when they discover a promising looking crevice. Once through, they discover an old English village where they meet a masked woman who has just robbed the local pub. She drops her bag of spoils in front of the two explorers and vanishes. Roxton and Marguerite enter the pub in an effort to find the rightful owners of the loot, when they are promptly arrested by the local prosecutor. When Roxton tries to escape, he is shot!

Veronica and Malone are captured by an angry mob who need slaves to mine their quarry. They soon discover that their fellow prisoners are not human; they are machines who are helping aliens repair their spaceship. Will the aliens discover that our heroes are human?!

Roxton and Marguerite return to the tree house to find it raided by a monkey. They follow the monkey to a cave where they find an amulet that leaves a mark of a dinosaur skull on their hands. Those infected with the mark soon begin to morph into their "animal" selves

Challenger and Marguerite discover an ancient Temple whose entrance is guarded by a carving of three armed warriors. When Marguerite falls into a pit of spikes, Challenger must leave her, to get help. As he leaves, the Guardians come to life. While Marguerite lies bleeding, she hallucinates. As Challenger is returning with the others, the Guardians attack them with invincible strength, but stop suddenly when they see Malone bleeding from a chest wound. While Veronica takes Malone home, the others hurry to the temple. When Roxton and Challenger reach her, Marguerite is baffled when they can see her hallucination, Adrienne. Following Adrienne's claims there is an exit from the plateau via the Temple, Challenger follows her map to the Temple's altar where he is confronted by William Maple White, a dead colleague whose journals had led him to the Lost World.

Marguerite and Roxton are enjoying an intimate moment, when suddenly the earth moves! They find themselves sprawled in the bottom of a pit, with a pirate's skeleton and his cursed treasure chest filled with a fortune in booty. Unimpressed by a little curse, Marguerite takes it to the Treehouse. Challenger and Malone find the pirate's journal, and decide to unravel his story. Traveling to the described inland sea, they are ambushed by pirate descendant Pappin, who seizes the journal. He sends his men to find the treasure, then shackles Malone in a tidal cave, leaving Challenger tied up in his shack

When Malone is slashed by a beast in the jungle, he shoots wildly. While looking for the animal, he and Veronica come across Danu, her childhood sweetheart, wounded, and warning them of the danger from this beast. Later that night, the team is disturbed by a howling animal, and discovers Danu gone and Malone feverish. Marguerite stays to nurse Malone, the others search for Danu, hoping to learn more about Malone's condition. Veronica leads them to his village, where only a witchdoctor and a few warriors armed with silver-tipped weapons, remain. The witchdoctor tells them that Danu has become a werewolf and must be killed by silver or fire, there is no cure. She gives Veronica a potion to delay the onset of Malone's transformation, then sends Challenger and Roxton to the Valley of Shadows where the werewolves live. Danu, wanting to transform Veronica to a werewolf like him, drives her towards the Valley of Shadows.

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.

Our heroes are astonished to see a British Navy dirigible flying low over their plateau. Malone, working away from the rest, is close enough to catch the last rung of its boarding ladder and clambers aboard. He finds the airship damaged and without crew, but as he opens a logbook, Capt. Askwith appears, and knocks Malone unconscious. As the airship flies beyond view, the others hear screams from a T-Rex hatchery. Luring the dinosaur away, they rescue, not Malone, as they expected, but Askwith! He claims not to have seen Malone. Marguerite is quite taken by him, and offers to bring him back to the Tree house to recover. Roxton, a little jealous, and very suspicious, accompanies them, as Challenger and Veronica follow the airship. They locate it in foothills nearby, and discover that the damage is not too serious, and enough fuel for three days flight off the plateau.