Roxton, Marguerite, Challenger and Malone are marked after touching an amulet, convincing them to return it to the cave.

A peaceful day of exploration turns deadly when a sudden explosion traps Marguerite and Roxton in an underground chamber. Their only hope for escape is Challenger, but the same explosion has left him with no memory of who he is, or what has happened to his friends. Meanwhile, a contest of friendly rivalry between Veronica and Finn leads to an enigmatic discovery at the Treehouse, as another memory from Veronica's childhood is literally uncovered. Faced with certain death, Roxton and Marguerite reveal emotions best left buried, so that even if they do survive their ordeal, there's a chance their relationship will not.

Two days before Challenger's latest attempt to leave the Plateau by balloon, Veronica and Finn encounter a strange phenomenon and are briefly transported into the post-apocalyptic future of New Amazonia. Soon after, Roxton finds himself being chased by 17th-century Conquistadors while Marguerite is captured by Druids determined to sacrifice her in order to avert a mysterious storm which is fast approaching. As different planes of reality continue to collide, Veronica at last realizes the time has come for her to fulfill her destiny as Protector and wield her mother's pendant-the Trion. But even as she prepares to sacrifice her life to save her friends, she does not know if she's made the right decision-for once the power of the Trion is unleashed, will it save the Plateau, or destroy it… ?

When the explorers enter an ancient temple, they release supernatural forces which threaten to destroy them.

When Challenger discovers the wreckage of a World War I transport plane, he's captured by its pilot, Lieutenant Drummond. Drummond has been stranded for five years since the crash, protecting the plane's cargo—a crate of iridium ingots stolen from the Royal Navy. Challenger is astounded to see the iridium because it had been intended for his secret wartime research. The sight of it prompts him to remember the night five years earlier, when he was questioned about the theft by two British intelligence agents working for MI5. Back on the Plateau, when Challenger and Drummond arrive at the Treehouse, Marguerite recognizes the iridium, too—she also was a suspect in its theft, and she recalls her own MI5 interrogation, the same night Challenger was questioned. Amazing twists and turns. We find out that there may be more than just coincidence that has brought our small group to the plateau.

The friends emerge from battle to find that one of their number is lost, and goons have enslaved a village.

While Roxton, Malone and Challenger are looking for a way off the plateau, Amazon women save them from an attack by a flock of pterodactyls.

An ancient map outlines an escape route; now the adventurers must prove to skeptics all they have seen.

Aliens capture Veronica and Malone, forcing them to work in the mines alongside androids that have developed humanlike emotions and individuality.

When Marguerite and Roxton kiss, the earth moves, and the explorers are launched on a wild treasure hunt.

A plane full of 21st-century tourists crashes in the jungle, bringing with it dreams of rescue.

Roxton saves a young woman and steps right into Balar's trap.

A woman who has saved the band from thirsty raptors will die if she cannot return immediately to the cave of the fountain of youth.

Marguerite recognizes as a trophy hunter a man who claims to be part of a Zoological Society rescue party.

Alex, a kobold, takes Roxton, Malone and Veronica prisoner; Holt is constructing a uranium generator to allow the kobolds to live above ground.

Roxton and Marguerite are jailed, accused of robbery after walking through a brilliant light on the far side.

During a thunderstorm visions of Summerlee, their lost colleague, lead the friends to the brink of destruction.

An escape route opens to the expedition when an airship lands on the plateau, but the mysterious pilot has other plans.

There's no escape for the Challenger Expedition when Captain Askwith's mysterious airship explodes in a fiery crash. But moments later, when Challenger, Roxton, and Marguerite appear on a British air station in 1915 -- on the same day the airship was launched on its final mission -- they realize they truly have taken the place of the captain's original crew. After two years of struggling to escape the Plateau, Challenger and his friends must now fight to return to it by once again taking flight on the doomed dirigible. At the same time, Veronica appears on the Plateau, and in a shocking confrontation with Captain Askwith, realizes she has her own mission to complete: pursue Askwith and somehow return him to his ship.

When Malone finds a knife, he is transported back to the East End of London in 1888, the scene of Jack the Ripper's brutal murders. In the nightmare of his visions, Malone sees his friends playing key roles in the crimes, both as conspirators and victims. Meanwhile, Veronica is approached by a famous British doctor, who enlists her to help find his missing knife. Could this man be Jack the Ripper? Or is it the Scotland Yard Inspector who runs into Roxton and Marguerite? Charmed by the Inspector and his claim to know a way off the plateau, Marguerite is eager to assist him in apprehending the Ripper. Marguerite realizes she could be walking into a deadly trap. Veronica is left to confront and defeat the infamous killer to prevent the murderous cycle from being repeated on the plateau.

Challenger, Malone and Veronica are exploring ruins on a riverbank, when a man stumbles out of the jungle in a hail of deadly arrows. Malone drags the wounded man to safety, who dies in their arms issuing a cryptic message to find a man named Pierson Rice. Challenger recognizes the name as that of a vain glorious hunter whom Roxton once held in high regard. The trio send a message to Roxton and Marguerite, then hurry on in search of Rice. Roxton is disgusted to learn that his one-time hero may be alive and well. Arriving at a native village, our heroes discover that Rice is far from peril -- in fact, he has made the natives his loyal subjects. With the help of his cold-hearted lieutenant, Rice plans to eliminate the queen and marry her beautiful daughter to consolidate his power.

When Roxton happens upon a hangman's noose dangling from a lonely tree in the jungle, he's suddenly transported back to the American West where he finds himself at the end of the rope. Facing him is Challenger, but in this world he's known as Sheriff Jack Challenger, a cruel lawman who neither recognizes Roxton nor listens to his plea of innocence. Saved by a rancher's widow, Roxton begins a strange journey to clear his name and find his way back to the Lost World. Along the way he runs into all of his friends but none of them recognize him -- Malone is a cold-hearted gunslinger, Veronica runs the local saloon and trading post, and Marguerite is the beautiful widow who saved Roxton's life. As Roxton struggles to make sense of it all, he is drawn to a final showdown in the saloon, where he must face his friends in a deadly shootout.

A mysterious visitor attacks Veronica, leaving an enigmatic ivory tile as his calling card. But when Marguerite finds the tile, she hides it from the others because only she knows what it means… one of the deepest secrets of her past has finally caught up with her, and now endangers her life and those of her friends. Back on the Plateau, with her friends facing death because of her actions in the past, Marguerite has no choice but to finally reveal the real reason she funded the Challenger Expedition, and what she has come to the Plateau to find.

At a haunted castle, the adventurers seem compelled to re-enact a romantic story of intrigue -- one that could end in death.

Dinosaurs are behaving oddly, but the crew knows something is really wrong when Marguerite is nice to everyone.