Financial disaster sends Tarzan back to Opar in search of treasure, where the priestess La and rival Oparians again place him in danger. An earthquake leaves him with memory loss while Jane becomes entangled with the disgraced Belgian officer Albert Werper and a band involved in ivory and slave trading.
Belgian officers, ivory trading and expeditionary travel place the adventure in the final phase of European colonial expansion in Africa. Opar remains one of Burroughs's great lost-world inventions, while the surrounding world of money, trade and imperial mobility gives Tarzan's treasure hunt a distinctly early-twentieth-century setting.
