"The Return of Tarzan" is the second "Tarzan" novel by Edgar Rice Burroughs.
Tarzan is 22 years old. The ape man, feeling rootless in the wake of his noble sacrifice of his prospects of wedding Jane Porter, leaves America for Europe to visit his friend Paul d'Arnot. On the ship, he becomes involved in the affairs of Countess Olga de Coude, her husband, Count Raoul de Coude, and two shady characters attempting to prey on them, Nikolas Rokoff and his henchman Alexis Paulvitch. Rokoff, it turns out, is the countess' brother. Tarzan thwarts the villains' scheme, making them his deadly enemies.
After a couple of twists - joining the French intelligence service, swimming for his life in the sea - Tarzan ends up in his "home" jungle, has several adventures - being captured and almost sacrificed, finding treasures, etc. - until he has to save Jane from a local tribe. She broke her engagement earlier, so Tarzan can marry her.
Edgar Rice Burroughs (1875-1950) was an American writer best known for his creations of the jungle hero Tarzan and the heroic Mars adventurer John Carter, although he produced works in many genres.