The Beasts of Tarzan was published in 1914 and is the third book in the sequence. Tarzan and Jane, now married, are living between London and the African plantation Tarzan has inherited from his Greystoke title. Their infant son Jack is kidnapped by the Russian spy Rokoff, who has escaped from prison and is plotting elaborate revenge. The kidnapping pulls Tarzan back into the African jungle, where he must enlist a band of unconventional allies to track the kidnappers and recover his son.
The titular beasts are the small army Tarzan assembles: the great ape Akut, several other apes, a panther named Sheeta, and a band of Mosula tribesmen. The novel is essentially one long chase across the West African coast and inland, with Rokoff staying just ahead of Tarzan from chapter to chapter. The eventual confrontation is satisfying. Korak, Tarzan’s son, becomes a significant character in his own right starting with the next book. The third novel sets up the larger family-saga structure of the series.