Plot summary
Tarzan, feeling rootless in the wake of sacrificing his prospects of wedding Jane Porter, [N 1] leaves the United States for Europe to visit his friend Paul d'Arnot. On the ship he becomes embroiled in the affairs of Countess Olga de Coude, her husband, Count Raoul de Coude, and two men attempting to prey on them, Nikolas Rokoff and his henchman Alexis Paulvitch. Rokoff is actually Olga's brother. Tarzan thwarts the villains' scheme, making them his deadly enemies.
In France, Rokoff repeatedly tries to eliminate Tarzan, eventually engineering a duel between the ape man and Raoul by making it appear that the former is Olga's lover. Tarzan refuses to defend himself in the duel, even offering his pistol to Raoul after the latter fails to kill him with his own. This gesture convinces Raoul of Tarzan's innocence. In return, he finds Tarzan a job as a special agent in the French ministry of war. Tarzan is assigned to service in Algeria.
A sequence of adventures among the locals ensues, including another brush with Rokoff. Afterward, Tarzan sails for Cape Town and strikes up a shipboard acquaintance with Hazel Strong, Jane's best friend. Also aboard are Rokoff and Paulovitch, who ambush Tarzan and throw him overboard.
Tarzan manages to swim to shore and finds himself in the coastal jungle where he grew up. He soon rescues native warrior Busuli of the Waziri tribe, which subsequently adopts Tarzan. After defeating a raid on their village by ivory raiders, Tarzan becomes their chief.
The Waziri know of a lost city deep in the jungle, from which they have obtained their golden ornaments. Tarzan has them take him there, but is captured by its inhabitants, a race of ape-like men, and is condemned to be sacrificed to their sun god. La, high priestess of the lost city of Opar is to perform the sacrifice and speaks the ape language Tarzan learned as a child. When the sacrificial ceremony is interrupted, she hides Tarzan and promises to lead him to freedom. But Tarzan escapes on his own, locates a treasure chamber, and rejoins the Waziri.
Meanwhile, Hazel reaches Cape Town, meeting Jane. With Jane is her father, Professor Porter, and her fiancé, Tarzan's cousin William Cecil Clayton. They are all invited on a cruise up the west coast of Africa aboard the Lady Alice, the yacht of another friend, Lord Tennington. Rokoff, now using the alias of M. Thuran, ingratiates himself with the party and is invited along. The Lady Alice eventually breaks down and sinks, forcing the passengers and crew into the lifeboats. The one containing Jane, Clayton and "Thuran" is separated from the others and suffers privations. Coincidentally, the boat makes shore in the same general area that Tarzan did.
The three construct a rude shelter and eke out an existence of near starvation for weeks until Jane and Clayton are surprised in the forest by a lion. Clayton loses Jane's respect by cowering in fear before the beast instead of defending her, but they are not attacked and discover the lion dead, speared by an unknown hand. Their hidden savior is in fact Tarzan, who does not reveal himself due to anger at seeing Jane with Clayton. Tarzan renounces any dealings with other humans, abandons the Waziri, and rejoins his original ape clan. Jane breaks off her engagement to William.
Later, Jane is kidnapped and taken to Opar by Oparians who were pursuing their escaped sacrifice, Tarzan. The ape man learns of Jane's capture and tracks them, saving her from being sacrificed by La, who is crushed by Tarzan's spurning of her for Jane. After searching for Jane, Clayton is incapacitated with a fever. Thuran abandons him to die and discovers other survivors from the Lady Alice who came to shore some miles away. He says that he is the sole survivor of his lifeboat.
Tarzan and Jane return to Jane's shelter, along the way encountering Busuli and some Waziri who have been searching for their king. At the shelter, Clayton is at the point of death. Before dying, he reveals to Tarzan and Jane that he knows Tarzan is the true Lord Greystoke. Tarzan and Jane return to his boyhood cabin and bury Clayton alongside his aunt and uncle. There, they encounter the castaways, who have been recovered by D'Arnot in a French navy vessel. Tarzan exposes Thuran as Rokoff and the French arrest him.
Tarzan weds Jane and Tennington weds Hazel in a double ceremony performed by Professor Porter, who had been ordained a minister in his youth. Then they all set sail for civilization, taking along the treasure Tarzan found in Opar. The Waziri receive gifts from the French and reluctantly accept the departure of their king.
