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.

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.

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.

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.

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 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….

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 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, 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 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.

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.

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.

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!

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.