Near Mondo Island in the South Pacific, the submarine Explorer hit a snag while performing a routine mission. A rockslide damaged the rudders, and repairs were deemed necessary before continuing. Meanwhile, the three high-ranking officers: Carl Nelson, Susan Watson, and Jiro Nomura, came ashore. As Carl and Jiro investigated the island, Susan stood guard over their hover car, but disaster soon struck. The gargantuan dinosaur Gorosaurus attacked the woman, and upon hearing her cries for help, something amazing emerged from the jungle. King Kong, an ape of astonishing size, placed the woman in the canopy of a tall tree to ensure her safety. Kong turned his attention to his powerful enemy and landed crashing blows on his foe. While Gorosaurus clenched his teeth on Kong's right ankle, the crew of the Explorer returned to the hover car and began to rush back to the submarine. Kong finally gained the upper hand and broke Gorosaurus' jaw, and then turned his attention toward the fleeing craft. Chasing after the hover car, the monster suddenly came face-to-face with the Giant Sea Snake. Tossing a boulder at the leviathan in hopes of distracting it, Kong gave the hover car enough time to escape. Upon defeating this new enemy, Kong continued to pursue his plans to procure Susan. Susan's beauty and voice soothed the beast as she pleaded with him to return to the island. The intelligent creature finally obeyed, and the Explorer returned to New York.

As the news of King Kong's existence soon became public, the international Judas Dr. Who concocted a plan abscond with the beast, for he wanted the mammoth ape to mine the highly radioactive Element X for his own diabolical purposes. The cruel doctor sent helicopters to drop ether bombs in order to trap the poor creature. The plan was a success, and an unconscious Kong began his long journey to the North Pole.

Shackled to a cement block in Dr. Who's hidden fortress, King Kong awoke to the sight of his robotic counterpart: Mechani-Kong. Using a hypnotic beam, Dr. Who placed his newly acquired slave under mind control and forced the creature to dig for Element X. The radiation of the rare substance was too strong however, and the mind control was completely severed. King Kong sought revenge! Ravaging the facility, he fled the Arctic and swam toward Tokyo, but the forces of evil were not far behind. Since Kong posed an immediate threat to the immense metropolis, the military was summoned to destroy the monster, but Susan intervened and made it known that the ape meant no harm.

Unfortunately, Mechani-Kong arrived on the scene and attempted to bring Kong under its master's command once more through its mind control technology. The attempt was thwarted, though, as Jiro Nomura interfered, shooting the device with a rifle. However, Mechani-Kong was not yet down and out, for it blinded Kong with its beams and took Susan in its grasp, as it began to climb Tokyo Tower. Dr. Who threatened to drop Susan if he did not receive full cooperation, but Kong pursued his mechanical doppelganger nevertheless. Susan was allowed to plummet to the ground below, but Kong managed to save his human friend and set her down. Mechani-Kong soon gained the upper hand however, and almost killed his organic counterpart. Thankfully, the controls on Dr. Who's ship were sabotaged, and the mechanized beast fell to the Earth and erupted into numerous pieces on the pavement. Kong, now eager to finish the fight, then attacked Dr. Who's ship, and the maniacal mastermind was crushed by his own equipment.

With his enemies destroyed and his friends saved, Kong returned to the peace and tranquility of Mondo Island.