Seeking to win the hand of fickle Gladys Hun-gerton, Edward Malone, a twenty-three-year-old newspaper reporter in London, interviews notorious professor of zoology George Edward Challenger. Challenger has startled the scientific world by asserting publicly that prehistoric creatures of the Jurassic period still exist.
Challenger and Malone travel to the wilds of Brazil with Professor Summerlee, a quarrelsome and skeptical comparative anatomist; Lord John Roxton, an accomplished hunter of big game; two “halfbreeds”; several South American Indians; and a faithful assistant named Zambo. Challenger and Malone overcome a series of vicissitudes to reach a mysterious volcanic plateau that had been upthrust from the jungle floor and now preserves unique flora and fauna. When a pterodactyl swoops down to grab some meat cooking on the group’s campfire, Summerlee realizes that Challenger was right.
Eventually, Challenger, Summerlee, Roxton, and Malone reach the top of the sheer-sided mesa, only to be stranded and seemingly trapped when their makeshift bridge is destroyed by one of the treacherous halfbreeds, who is promptly shot. While on the summit plateau, Challenger and the others discover docile iguanodons, rapacious pterodactyls, dangerous bipedal carnivores, and a number of other Mesozoic creatures. Eventually, they also discover primates of two kinds: ape-men who are apparently the “missing link” called for by evolutionists, and their successors, early human beings. The two hominid groups appear to be constantly at war. Intervention by Challenger and his well-armed group ensures the extermination of the ape-men. A grateful human prince directs Challenger to a cave escape route that takes him and his party down from the mesa.
The expedition eventually returns to London, where Challenger confounds his remaining critics by displaying a carefully preserved pterodactyl. Malone, now a hero, returns confidently to Gladys only to find that she has married a wimpish legal clerk. Malone and the adventurous Roxton determine to revisit their secret prehistoric world in South America.