A mad scientist builds Mechani-Kong, a giant robot ape meant to mine a rare radioactive element, but when the machine breaks down he instead captures and hypnotizes the real King Kong to do the job for him. After Kong breaks free of the scientist's control, he swims to Tokyo, where he battles his mechanical double atop Tokyo Tower. A Toho co-production loosely tied to the Rankin/Bass cartoon continuity, directed by Ishirō Honda.