In attempting to track Jane, Tarzan has come to a hidden valley called Pal-ul-don filled with dinosaurs, notably the savage Gryfs which are Triceratops that are omnivorous and stand 20 feet tall at the shoulder, have claws on their front legs, and Stegosaurus-like plates on its back.

The lost valley is also home to two different adversarial races of tailed human-looking creatures: the hairless and white-skinned, city-dwelling Ho-don and the hairy and black-skinned, hill-dwelling Waz-don.

Tarzan befriends a Ho-don warrior and the Waz-don chief actuating some uncustomary relations.

Her German captor becomes dependent on her due to his own lack of jungle survival skills.

With the aid of his native allies, Tarzan continues to pursue his beloved, going through an extended series of fights and escapes to do so.