Doctor Robin Doyle returns to the jungle with her nephew Ian, a bookish child with few friends who spends his time collecting butterflies. While Robin and the Professor spend some quality time "spooning", the task of entertaining Ian falls to Tarzan, whom Ian sees as a much-needed role model. Lacking any other experience, Tarzan fills the day with activities he enjoyed as a child, and it's not long before the boy has discarded his formal trappings for a loincloth. None of this sits quite well with Jane, who worries about the dangers of a small child swinging recklessly from tree to tree—and what the good doctor will say when she finds out.

A violent thunderstorm has Tarzan, Jane and the rest of the gorilla family seeking shelter in nearby caves. Along the way, Tarzan feels unsure that he can protect the family as well as Kerchak did. Upon reaching the cave and thinking they are safe, they realize they are in the same cave where Tublat lives in. Tarzan is no physical match for Tublat and must use his superior cunning and ingenuity to defeat him.