Passenger Sir Henry Vining (Richard Haydn) and his treasurer (Ronald Long) scream in horror.

On his signal, pilot Jacques (Fabian), ascends the balloon using a pressure gauge that ensures no loss of gas or ballast.

Traumatized by their "near-disaster", Sir Henry, head of the Royal Geographic Society, and his treasurer refuse to fund Jupiter's exploration of East Africa, and walk out on the professor after landing.

American publisher Cornelius Randolph comes to the rescue: He will back the venture if his star reporter and nephew, Donald O'Shay (Red Buttons), joins the crew.

On the day Fergusson intends to set sail for Africa, he learns that his expedition is halted and that plans have been changed.

At the British Parliament, the prime minister commissions Fergusson to defeat a convoy of slave traders heading toward uncharted land near the Volta River in West Africa.

However, he did not calculate the Queen sending along Sir Henry, who proclaims himself to be the "expert on Africa" and demands to be called the "General".

While Fergusson meets with the British Consul in Zanzibar, Jacques spots O'Shay helping to free slave girl Makia (Barbara Luna), fighting off traders and disrupting her sale.

Landing in a jungle, they learn Makia stowed away to join them, they also adopt a wild chimpanzee called "The Duchess".

There, Ahmed, a slave trader (Peter Lorre), enters, offering for sale a kidnapped American teacher, Susan Gale (Barbara Eden).

They blame him for putting the balloon in the path of attacking natives, and releasing its anchor, causing it to drift away.

In Timbuktu, Fergusson, Susan, and the General are imprisoned as infidels, and set to be thrown from the highest tower, while Makia is put up for sale.

Jacques, Ahmed and O'Shay, in disguise, purchase Makia from a slave trader (also played by Billy Gilbert).

In 1955, Tony Curtis announced plans to produce and star in a version of the novel for his own company, Curtleigh, and hired Kathleen Dormer to write a script.

[7] In June 1961, Irwin Allen, who had made The Lost World announced he had secured rights to the novel after six years of negotiation and would likely make the film at 20th Century Fox.

There was a race between two producers attempting to be the first to film the story: Allen and the Woolner Brothers, who made Flight of the Lost Balloon (1961) directed by Nathan Juran.

[1] Allen wanted to make the film as a straight adventure movie with accent on comedy and youthful romance.