After detailing the Claytons' doomed voyage to Africa, their stranding there, their son's birth, and their deaths, the book centers on Tarzan's adoption by the she-ape Kala and his upbringing. Feeling alienated from his peers due to his physical differences from them, he discovers his true parents' cabin, where he first learns of others like himself in the books they had owned, which he eventually teaches himself to read.
On his return from one visit to the cabin he is attacked by a huge gorilla ("Bolgani" in Mangani) which he manages to kill with his father's knife, though terribly wounded in the struggle. As he grows up, Tarzan becomes a skilled hunter, exciting the jealousy of Kerchak, the ape leader, who finally attacks him. Tarzan kills Kerchak and takes his place as "king" of the apes.
Later, a tribe of black Africans settles in the area, and Kala is killed by one of its hunters. Avenging himself on the killer, Tarzan begins an antagonistic relationship with the tribe, raiding its village for weapons and practicing cruel pranks on them; they, in turn, regard him as an evil spirit and attempt to placate him. Subsequently, a new party of whites is marooned on the coast, including Jane Porter, the first white woman Tarzan has ever seen. By the kind of wild coincidence typical of Burroughs' stories Tarzan's own cousin, William Cecil Clayton, unwitting usurper of the ape man's ancestral English estate, is also among the party. Tarzan spies on the newcomers, aids them in secret, and saves Jane from the perils of the jungle. Absent when they are rescued, he is introduced further into the mysteries of civilization by the Belgian Paul d'Arnot, whom he saves from the natives. D'Arnot teaches Tarzan French, teaches him how to behave among white men, and guides him to the nearest colonial outposts.
Later, Tarzan travels to Jane's native Baltimore, Maryland only to find that Jane is now in the woods of Wisconsin. Tarzan finally meets Jane in Wisconsin where they renew their acquaintance and he learns the bitter news that she has become engaged to William Clayton. Clues from his parents' cabin have enabled d'Arnot to prove Tarzan's true identity; informed of this, a word from him can ruin Clayton. Tarzan chooses rather to conceal and renounce his heritage for the sake of Jane's happiness, and on that note the novel ends.
-Courtesy of Wikipedia.com