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.