Tarzan is summoned to an unnamed Asian country to protect Kashi (Ricky Der), the youthful heir to the throne, from his evil uncle, Khan, played by Tarzan veteran Woody Strode.
Tarzan and Jane have left Africa, married and settled in London. Their pre-teen son, Jack, dreams of jungle adventures like his father's, but is discouraged by his parents. He sneaks away to see a trained ape called Ajax (in reality, Akut, an old friend from Tarzan's youth). The ape's trainer is really Ivan Paulovich, an old enemy of Tarzan's, who is looking for a way to enact vengeance. He kidnaps Jack and takes him to Africa.
John and Alice Clayton (Lord and Lady Greystoke) are marooned on the coast of Africa, where their son, John Clayton, Jr., is born. The baby is orphaned when both parents die of a mysterious disease, but is adopted by Kala and Kerchak, members of the tribe of Brown Apes.
Two hunters come into the jungle intent on killing as many animals as they can in order to get barrels of animal fat, lion skins and elephant tusks. Tarzan tries to help a baby elephant, one of their first victims. He takes the elephant to an animal doctor and his female assistant, who have pitched their tents in the jungle to do business. The hunters turn up and pretend they are photographers and have the doctor escort them to where the animals are. They leave the doctor and start killing animals. His assistant finds out what they're really up to and goes after them but needs Tarzan's help when she stumbles into quicksand. He rescues her, and she says she needs a bath so Tarzan throws her into the river.
The film makes use of a frame tale to present three self-contained "episodes" via flashback. Jane and Tarzan's first wedding anniversary has arrived, and Jane is trying to find a suitable present for her husband, with the help of the elephant Tantor, and the gorilla Terk.
Lord Greystoke (Tarzan) returns to Africa, with Lady Jane and friend Albert Werper, in order to return to Opar. He needs the treasure of Opar in order to secure his estates in England. Werper, however, is actually interested in the gold himself. He is in league with Arab slave trader Achmet Zek who wishes revenge on Tarzan and Lady Jane for himself.
Tarzan is called to Brazil by an old friend, The Professor (Paulo Gracindo) to help stop the Jaguar Cult, led by Barcuma (Rafer Johnson), from destroying native villages and enslaving the survivors in his search for diamonds. Tarzan is assisted by Captain Sam Bishop (Jan Murray), a riverboat pilot, and Bishop's young ward, Pepe (Manuel Padilla Jr.), as well as Baron (a lion) and Cheeta (a chimpanzee). On their way they encounter Dr. Ann Philips (Diana Millay), who has witnessed the destruction of a village, and wants to continue fighting a plague by giving much-needed inoculations to natives who live along the Amazon River.
Beautiful but deadly Lyra the She-Devil and her ivory-hunting friends have discovered a large herd of bull elephants and plot to capture them, forcing an East African native tribe to serve as bearers. Their ivory poaching plans meet opposition when Tarzan gives his deafening jungle cry. The tusked creatures come running, stomping all over Lyra's plans.
Tarzan is called to India to save three hundred elephants, that will be drowned if a dam is opened to create a man-made lake to power an electric plant. Tarzan is pitted against two engineers who ignore the catastrophic results their work will create.
At home in Africa, Tarzan assists Myrna, a photojournalist, and Ken, her associate, in their search for Erik Brunik, a thirteen-year-old boy lost in the jungle since he was seven years old. Tarzan is assisted by his friend Buhara, whose brother Nagambi does not wish the boy found, and attempts to kill him before Tarzan saves the day.
Jungle medics Dr. Sturdy (Carl Benton Reid) and his daughter Anne (Jil Jarmyn) are opposed by witch doctor Futa (James Edwards) of the Nagasu tribe, who regards their work as a threat to his own livelihood. Futa incites the tribe to waylay Anne's fiance Dr. Ken Warwick (Harry Lauter), who is saved by Tarzan (Gordon Scott). Later Tarzan and his adopted son Tartu (Rickie Sorensen) enlist the doctors' services on behalf of Jane (Eve Brent), suffering from appendicitis. Futa hypnotizes Moto (Nick Stewart), a native assistant of Sturdy, to murder Jane, but Tarzan thwarts the plot. Learning that the young Nagasu chief (Roy Glenn) is sick, Tarzan attempts to persuade them to let Sturdy treat them. Seizing his chance, Futa has the ape man taken captive and condemned to death. To restore his own credentials, the witch doctor then undertakes to cure the chief himself, hedging his bets by having his henchman Ramo (Woody Strode) steal medicine from Sturdy. Unfortunately, Ramo purloins a poison by mistake. Freeing himself, Tarzan intervenes and prevents the administration of the poison to the chief; Futa then swallows it himself to demonstrate that there is no harm in it — and dies. Dr. Sturdy is consequently called in, successfully curing the chief.
Tarzan and Jane are traveling to Paris to help his old friend Countess de Coude, who is being threatened by her brother, Nikolas Rokoff. Rokoff has Tarzan tossed overboard. He survives, comes ashore in North Africa, and goes to Paris to search for Jane.
After a ruler dies, tradition dictates the new ruler must accomplish a series of harrowing challenges whilst competing with other aspirants. One of them, a young prince (Robin Aristorenas) engages in the contest, but evildoers plan the young prince's demise. Tarzan protects him while ensuring he meets the tests.