After leaving Jane Porter, Tarzan attempts life in Europe, becomes involved with the French Secret Service and disrupts a Russian espionage plot. A sea voyage returns him to Africa, where he joins the Waziri, discovers the treasure of the lost city of Opar and is drawn once more into Jane’s fate.
Parisian espionage, ocean travel and colonial routes give the story a distinctly pre-First World War atmosphere before the action returns to Burroughs's imagined African interior. Opar is a lost-world invention, but the movement between European capitals, steamship networks and colonial Africa roots the adventure in the international world of the early twentieth century.
