Prof. Challenger (Wallace Beery) just recently returned from an exploratory expedition in South America. There he found a remote region of the Amazon where dinosaurs still roam the earth. But he had to leave a missing colleague behind and wants to return. Newspaper owner Edward E. Malone (Lloyd Hughes) is naturally skeptical until he receives a diary from Paula White (Bessie Love). Convinced he can use the exploration for his newspaper, he puts together another expedition. Once there in the jungles of Brazil, the discover that the dinosaurs do roam free and there are also ape-like people living among them. Not satisfied with a story only, Malone decides to trap a dinosaur to bring back to London to show the world, hoping to get rich. But his plans fall apart when the creature escapes and causes havoc.