The book opens with Tarzan, Jane and Korak returning from the land of Pal-ul-don from the last book. They come upon an orphaned lion and Tarzan decides to adopt him. They name him Jad-bal-ja which in the language of Pal-ul-don means golden lion.
Years later the lion cub grows into a strong lion. Tarzan meanwhile comes upon a safari in this lands. This safari lead by Flora who was in the employ of Tarzan and learned of the lost city of Opar. She has put together a safari to rob its gold. They drug Tarzan’s coffee and leave him to be captured by the Oparians.
While captured Tarzan finds out the La the high priestess has been deposed and schedules to die on the sacrificial alter with Tarzan. Tarzan and La escape to the land beyond Opar. This land is ruled by intelligent gorillas that rule over servile men. Tarzan is joined by his lion Jad-bal-ja and together they lead a revolt of the men against their gorilla overlords. Then they restore La to her priestess position in Opar and defeat Flora’s safari.
The ninth book in the series is another strong entry in the series. This marks where Tarzan starts to become a sort of aimless wanderer around Africa having adventures among lost civilizations.