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.

Our adventurers recover an ancient map showing the escape route from the Lost World. Knowing they will face sceptics 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?

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.

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.

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 Treehouse 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.

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.

An unsettling dream and a ghostly encounter convince Veronica that Malone is trapped in the spirit realm and needs her help to escape. At the same time, Assai and Challenger investigate a mysterious symbol burned into a field of grass, which Assai identifies as the mark of Saros, a bloodthirsty warlord who was overthrown by the Zanga and died swearing to return from the grave to wreak vengeance on the living. Back at the treehouse, Marguerite and Veronica use a Ouija board to contact Malone, which results in a frightening display of poltergeist-like activity, and a brief, but terrifying manifestation of Saros. Assai is convinced that any new attempt to rescue Malone from the spirit realm threatens to release Saros instead.

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.

Challenger develops a new way to create lift in the balloon. All go along for a test flight, but the balloon is drawn into violent turbulence then crash-lands inside the vast caldera of an extinct volcano where our heroes find themselves trapped in a world beneath the earth's surface. With the balloon damaged and the supply of iron lost, our heroes can only survive for a matter of days in this hot and hostile environment.

Aleece, a strong-willed female warrior-in-training, hurries to the rescue. In exchange for a ride in the balloon she offers to help replenish the iron that is needed. Malone accompanies her to a mine, but instead of raw ore, her plan is to steal from the supply of a vengeful exile named Arjax. After being caught by Arjax, Malone and Aleece face death unless they lead Arjax back to the balloon.

When Keeran Raiders attack, a deadly poison dart forces Malone to relive a long-suppressed memory-his baptism of fire as a battlefield correspondent in World War I. Caught up in this nightmarish hallucination, Malone is once again an untried reporter cut off from Allied lines when an enemy advance pushes deep into No Man's Land. When the three battle-weary British soldiers who've been assigned to escort him are picked off by enemy action, the young reporter who's never fired a gun must take up arms to save his own life and the life of a wounded sergeant.

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.

When a lost archaeological expedition discovers a mysterious burial urn, the young student who opens it suddenly collapses in convulsions. Though she quickly recovers, Professor Hamilton, the expedition's leader, suspects she's contracted a disease from the urn's skeletal remains. He believes that's the only rational explanation for the inscription on the urn, warning that an evil demon is imprisoned within.

But the next day, Roxton and Marguerite discover the expedition's camp has been torn apart, and that of all the archaeologists only two survive-Hamilton and his rival, Professor Campbell. In a tense standoff, the two men claim the other is possessed by the demon. Roxton's and Marguerite's intervention only succeeds in making the archaeologists suspect the demon has jumped into one of the two explorers.

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.

Led by a dream, Veronica touches her mother's pendant to a stone monolith. A flash of mysterious energy knocks her unconscious, causing her to relive her last days with her long-lost parents as a young girl. When she awakes, she's shocked to realize her new memories don't match what she's always remembered of that time.

With the fate of her parents no longer unknown, Veronica is at peace, though she realizes a larger mystery is still to be revealed-her mother's pendant is somehow the key to her own destiny… and that destiny is fast approaching.

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… ?