A giant ape named Kong lives peacefully on Mondo Island, where he is discovered by a United Nations submarine crew. Led by Commander Carl Nelson, the crew is conducting geological surveys when they encounter Kong, who saves Lieutenant Susan Watson from a dinosaur attack. Meanwhile, the villainous Dr. Who creates a giant mechanical replica of Kong, Mechani-Kong, with plans to use it for mining a highly radioactive element called Element X in the North Pole. However, Mechani-Kong fails due to the intense radiation and Dr. Who sets his sights on capturing the real Kong to complete his mission.

Dr. Who and his team manage to kidnap Kong and take him to the North Pole. They brainwash him into assisting with their plan to obtain Element X. Commander Nelson, Susan Watson, and their crew track Dr. Who's operations, determined to rescue Kong and stop the villain's dangerous scheme. They face numerous obstacles, including confrontations with Dr. Who's forces and the unpredictable behavior of a confused and manipulated Kong. The situation escalates, leading to a dramatic showdown involving both the real Kong and Mechani-Kong, with stakes that could impact the world's safety.