Summary (from Ballantine Books blurb): 
Now that he was the rich Lord Greystoke, Tarzan became the target of greedy and evil men. His son was kidnapped, his wife had been abducted, and Tarzan was stranded on a desert island where he seemed helpless. but with the help of Sheeta, the vicious panther, and the great ape Akut, Tarzan began his escape. Together with the giant Mugambi, they reached the mainland and took up the trail of the kidnappers. Tarzan sought his wife and his child—and he sought such vengeance as only a human beast of the jungle could devise. But the men Tarzan sought had fled deep into the  interior—and the trail was old and well-hidden.

Paul d'Arnot: French naval officer, Tarzan's friend in Paris
Tarzan: John Clayton, Lord Greystoke, Lord of the Jungle
Nikolas Rokoff: Tarzan's enemy
Alexis Paulvitch: Rokoff's assistant
Jane Porter Clayton:  Tarzan's wife, Lady Greystoke
Jack Clayton: Son of Tarzan and Jane
Carl: The Claytons' servant in London, kidnapping accomplice
Sven Anderssen: Swedish cook aboard the Kincaid
Molak, Akut: great apes (Mangani) on the island opposite the Ugambi river
Sheeta: panther who befriends Tarzan after being rescued
Mugambi: giant chief of the Wagambi who becomes Tarzan's lifelong friend
Kaviri: chief of a tribe on the Ugambi river
M'ganwazan: cannibal chief on the Ugambi, Rokoff's accomplice
Tambudza: oldest wife of M'ganwazan
Buulaoo: son of Mganwazan by a younger wife
Gust the Swede, Momulla the Maori, Kai Shang of Fachan: Cowie mutineers 
Schneider, Schmidt, Jones, Sullivan: mate and sailors from the Kincaid
Esmeralda: The Claytons' maid in London
Mosula woman: Mugambi's betrothed