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.

While searching for the missing Malone, Marguerite is saved from a cannibal attack by a dashing trio of bandits. Their leader, the elegant Francois Locke, invites her to join his band of thieves. Marguerite declines his offer, only to be presented with proof that Locke can give her what she desires most - a way off the Plateau. Meanwhile, as Challenger, Roxton, and Veronica search for Marguerite, they discover evidence that the bandits are something other than human. Even worse, they receive a ransom note from them, demanding Marguerite's jewels in exchange for her release. But when they deliver the ransom, they're shocked to see that Marguerite isn't a prisoner at all - she appears to have joined Locke's group!

While exploring a mysterious dinosaur bone yard, Roxton is attacked by a charging Ttriceratops and kills it, not out of necessity but in anger. However, the bone yard is actually a sacred animal burial ground, protected by a beautiful, half-human, half-dinosaur guardian named Oseena. To punish Roxton for his crime, Oseena curses him to become the prey in a hunt that will end only with his death. Shaken by his encounter with Oseena, Roxton returns to the treehouse, but the hunter tracks him relentlessly and then captures Marguerite, using her as bait to lure Roxton into a deadly trap. Roxton returns to Oseena's burial ground to confront the hunter and save Marguerite.

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 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.

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 a powerful witch named Dame Alice feels threatened by Challenger's science, she calls upon her two beautiful acolytes to help undo his power. In order to earn full witchhood, the two must lure Challenger's ""guards"" - Roxton and Malone - to the witch's castle while she goes head to head with the ""wizard"" - Challenger - herself. While the two young witches distract Roxton and Malone, Dame Alice visits the Treehouse for a visit. In spite of Marguerite's protests and warnings, Challenger is intrigued by the witch's power and too easily lowers his guard. When Dame Alice sabotages Challenger's newest invention and almost kills him, it is only Marguerite's quick thinking that saves the scientist from his own folly. But in the end it is not Challenger's life that is in danger, but the lives of Roxton and Malone….

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.

When a blindingly bright meteor strikes the Plateau, Challenger, Roxton, and Marguerite set out to investigate the impact site. But the closer they get, the colder the temperature becomes. As the explorers turn back, they discover what appears to be a victim of the intense cold - a beautiful, blue-skinned woman, unconscious and nearly frozen. To save her life, the explorers take her back with them. When the frigid temperatures reach the Treehouse and all attempts to warm the woman makes her condition worse, Challenger suspects that things are not as they appear. Roxton and Marguerite are attacked by a group of blue-skinned male warriors and the truth becomes clear - the heat-absorbing meteorite now buried in the Plateau is the first step in a terrifying invasion of creatures who need the cold to survive.

Ambushed in the jungle, Roxton narrowly escapes with his life only to learn that he has apparently cheated death once too often. The Grim Reaper, in the guise of a dark seductress - is determined to add his soul to her collection. Transported to her domain - a bleak and desolate wasteland - Roxton must face a series of challenges if he hopes to get out alive. And to make the game more interesting, Death raises the stakes by putting the lives of his friends on the line as well. Confronted by shifting rules and deception, Roxton cannot hope to win. At every turn, Death torments and goads him, encouraging him to abandon his friends to save himself. Round one goes to Death, rounds two and three as well, and with growing horror, Roxton loses Challenger, Veronica, and finally his beloved Marguerite to Death's netherworld inferno.

Alone in the jungle, Veronica hears piano music and follows it to its source - a 19th century German village that has suddenly appeared in a fog choked valley. To her surprise, the handsome musician, Thomas Ducart, announces that he wrote the beautiful melody for her. Flattered by the musician's attention, Veronica takes him to the Treehouse, but Challenger is concerned. He fears that Ducart's village may be unstable, and Veronica could disappear into another dimension if she returns to the village with Ducart. Even more disturbing, are Challenger's ill feelings about Ducart's designs on Veronica, but Challenger's warnings only drive the beguiled Veronica further into Ducart's passionate embrace.

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.

Using the Plateau's mysterious energy lines as a source of power, Challenger constructs a machine to send the explorers back to London. But when he, Roxton, and Marguerite find themselves in the same place they started from, they conclude the machine is a failure and head back to the Treehouse-only to discover the Treehouse is gone! While investigating what else has changed, Roxton is captured by slavers with automatic weapons and stripped-down cars, and learns the shocking truth-he and his friends are in the year 2033, eighteen years after an apocalyptic war devastated every place on Earth except for the Plateau.

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.

Challenger, Roxton, and Marguerite take Finn to a cave where one year earlier a blinding light opened a doorway to another reality. Once inside, the explorers witness an eerie apparition of a man Finn recognizes and fears. But when Finn races from the cave, the three figures who follow are not her friends-they're Kayle, Una, and Rixxel, three demons who have taken the place of Challenger, Roxton, and Marguerite. If the demons can remain on the Plateau for two days, they will permanently replace the explorers, and Kayle will be free to bring chaos and destruction to the world. In the final deadly showdown between Finn and the demons, Finn must make the decision of her life-save the future or save her friends. Until an unexpected sacrifice changes everything…

Hoping to end starvation, Challenger becomes the first human subject to test his new experimental substitute for food. But his nutritional beverage is not as successful for him as it was for his lab mice, and he quickly becomes obsessed with discovering the reason why. Then obsession leads to madness as Challenger is confronted by two opposing hallucinations. The first is a vision of himself as a young, driven scientist. The second is his beloved wife, Jessie, as he left her in London three years earlier. Unconscious and near death, Challenger is finally discovered by his friends. But will their limited medical knowledge be enough to reverse the ravages of his experiment, without placing him in even greater peril?

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.

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… ?