When the Professor's rival, Samuel T. Philander, visits Africa, he must come up with something spectacular to become famous on before Philander. That's when Tarzan tells them about Pellucidar, an underground world where dinosaurs live. However, Philander follows them there and takes pictures of the dinosaurs. The Professor, having no camera with him, attempts to best Philander by taking something else with him.

When Terk and Tantor accidentally spill some of the fluid from the giant flowers the Professor was studying onto a few beetles, it makes them giant themselves. To stay out of trouble, they keep it a secret. But how can you keep a couple of huge beetles a secret?

Tarzan and Jane return from a trip to the Waziri village to find the Professor missing and his camp in ruin. Jane momentarily fears the worst, but soldiers on with Tarzan in an attempt to determine her father's whereabouts and condition—a pursuit impeded by the hordes of apparently mad animals, including Terk and Tantor, destroying everything in their path and pleading for the cessation of a mysterious, unheard ringing.

The leopard men attack the treehouse and, rather than retrieving Tarzan (as the gang expects), make off with Jane, and gas the others. Once conscious, Tarzan, Tantor, Terk and the Professor set off for Opar to rescue her, only to find Queen La, staffless and at the mercy of a leopard, begging for help. Despite the Professor's warning, Tarzan intervenes and forges a temporary alliance with La to free his wife from La's rebelling minions. However, he is unaware of the true intentions of La and the leopard men.

A logger's daughter and workers fall ill with a dangerous disease. Tarzan seeks to obtain a cure for the disease, only to find out the cure may have been destroyed by their irresponsible logging.

A film crew arrives in the jungle to shoot an action movie. Tarzan, being unaware of this, interferes in the process, causing him to appear in the scenes unintentionally. The film's male lead actor becomes jealous after being replaced by Tarzan and attempts to destroy the footage, causing a huge fire at the trading post.

While the gang is setting up a surprise croquet game for the Professor, Jane encounters an ill-looking fawn. Upon touching the fawn, the soul of Queen La enters her body. Failing to return to Opar by herself, La turns to Tarzan, who senses something wrong right away. Instead, she turns to Dumont for help. Can the aid of Usula, the Waziri elder, bring Jane back before La retrieves her staff and brings Opar to life again?

Philander returns to Africa with two British thugs to capture "Tarzan: The Missing Link" in a last-ditch effort to pay off the thugs. While there, they meet up with the Professor and Philander attempts to convince the thugs that the Professor is Tarzan.

Zutho, a shady mandrill from Tarzan's past, resurfaces, demanding a favor he claims is owed for keeping a 20-year-old secret. This results in Tarzan having to do everything Zutho tells him to. What secrets does Zutho know to gain such a hold over the lord of the jungle?

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.

Two sneaky men named Johannes Niels and Merkus come and want Tarzan to take them to the volcano on the other side of the jungle to look for diamonds. Tarzan agrees as long as he gets a diamond for Jane in return. Little does he realize that the men are not planning to keep up their side of the bargain when the diamonds are collected—or that his friends are following them.