The film was an adaptation of episodes of Rankin/Bass and Toei Animation's The King Kong Show cartoon series. As with King Kong vs. Godzilla, Eiji Tsuburaya served as director of special effects.
An evil genius named Dr. Hu creates a robotic version of King Kong, named Mechani-Kong, in order to dig for a highly radioactive element called "Element X", found only at the North Pole. The extremely rare compound, once unearthed, will be sold to an Asiatic country (never identified in the film) and used to give said country nuclear domination of the world. The Doctor, along with a benefactor from the unidentified nation known only by the alias "Madame Piranha", watch as Mechani-Kong enters an ice cave and begins to dig into the glacier. However, as the robot digs, the unbelievable radiation produced by the glowing substance destroys its systems and shuts it down. Meanwhile, a submarine from the United Nations is damaged and forced to weigh anchor off the coast of Mondo Island, an island where, according to legend, the real King Kong resides. As it so happens, the sub's Commander Carl Nelson has spent many years studying the legend of Kong and is all to pleased to venture ashore to explore, along with with Lt. Commander Jiro Nomura and Lt. Susan Watson. Once on the Island, the crew see an old man atop a hill shouting at them to leave the area, for it is taboo to enter the territory of Kong. Nelson and Nomura go to confront the old man, leaving Susan alone with their landing craft. However, no sooner have the men left then a gigantic theropod dinosaur (later dubbed Gorosaurus in the film Destroy All Monsters) emerges from the forest and makes to attack Susan Suddenly, from out of a nearby cave, a roar is heard, and a few seconds later, King Kong himself emerges, bellowing and beating his chest.
Seeing Susan, he realizes she is in danger and places her in a tree. Then, Kong attacks Gorosaurus with all he has. Unfortunately, the bipedal predator possess a powerful "kangaroo-kick" that floors Kong several times and prevents him from getting to close to inflict serious damage. As the two titans duke it out, Nelson and Nomura return and, with Susan in tow, escape in their hovercraft. Behind them, Kong finally defeats Gorosaurus by breaking its jaw. He follows the hover-craft to the coast of the island just in time to see a Giant Sea Snake heading for them. Kong dives into the water and grabs the snake, buying time for the crew to return safely to the sub. The giant ape then defeats the huge serpent and swims over to the sub. He begins to shake it and bang on the hull, hoping Susan will appear again. Knowing she is what Kong wants, Susan volunteers to exit the sub to try to calm him down. She succedes, and after saying goodbye to a crestfallen Kong, she returns to the sub and the crew leaves for New York.
Once in America, the submarine crew relates their amazing discoveries on Mondo Island to the United Nations. They also state that the sub will be returning to the island to study Kong and his fellow monsters on the island. However, they are unaware that Madame Piranha is at the meeting, and after it ends, she sneaks into the ladies restroom and contacts Dr. Hu. She relates the details of the crew's discoveries, and she and Hu begin to hatch a plan. A few days later, Dr. Hu arrives on Mondo and a fleet of helicopters fly out and attract Kong's attention. They drop gas bombs around the great ape, and the ether soon knocks him out cold. The helicopters then lower large shackles down, and a ground crew secures them to Kong's wrists and ankles. Suddenly, the old man erupts from the jungle and points at the the now secured ape, and as he attempts to get answers from Dr. Hu (unfortunately in a language only the speaker can understands), the evil scientist shoots him three times and leaves him in the underbrush to die. As he departs, the four helicopters lift King Kong from Mondo Island and lower him into the cargo hold of their huge ship. They then head back to the North Pole. Soon after, the United Nations sub returns and the trio of Commander Nelson, Lt Commander Nomura, and Lt Watson venture onto the island. They discover evidence of something nefarious, and are unable to locate Kong. What they do find, however, is the old man bleeding in the bushes. As the islander lays dying in Susan's arms, he tells Carl, who can understand the language, that "An oriental skeleton, a devil with eyes like a gutter-rat, kidnapped Kong and took him away into the skies. He then dies, but he has told Carl all he needs to know: Kong was kidnapped by Dr. Hu, an old "friend" of Carl's. In fact, Hu's Mechani-Kong was built using blueprints based on Nelson's own detailed diagrams of the real Kong. The Doctor had stolen the drawings and used them to create a robot that he believed would secure for him the Element X. However, the robot had failed, and now Hu planned to use the real Kong to do his bidding. However, in order to do that, he needed to put the next part of his plan into action. He sends several of his minions to Mondo Island who, posing as the Japanese SDF (Self Defence Force), collect Carl, Jiro, and Susan, claiming that Kong has swum ashore at Tokyo. The trio are suspicious, but can do nothing as they are flown off to the North Pole.
Menwhile, Dr. Hu decides to try another method of controlling Kong. His reason for kidnapping the three crew members were not only for their familiarity with Kong, but for the ape's relationship with Susan Watson in particular. On Mondo, Kong had been so infatuated by Watson, that he began to listen to her and do what she asked. Although Dr. Hu believed that he could use this connection to get Kong to extract the Element X, he is not willing to wait for the prisoners to arrive and puts an alternative idea to the test. In the cage where the still unconscious King Kong lies, workers attach both a receiving speaker and camera to the beast's ears. When Kong awakens, his first sight is a flashing light that soon places him in a state of hypnosis. From the speaker, the voice of Dr. Hu commands Kong to enter the cave and dig out the Element X. Kong complies and ventures into the cave and begins to dig. However, the hypnotized Kong soon snaps out of it, and tears both the speaker and camera off of his ears. He then turns around and attempts to return to the base, but Hu orders the gate shut, and Kong is trapped in the cave. Soon after, Carl, Jiro, and Susan arrive and are greeted by Dr. Hu. He explains his plans and requests their assistance. All three refuse, and are put into a holding cell. A few minuites later, Carl is released and brought to the room of Madame Pirahna, who explains her view of the whole situation. As she attempts to buy Carl off, Dr. Hu enters and promptly breaks up the meeting. Only a few minutes after Carl is returned to the cell, he is once again summoned, this time by Dr. Hu. In an attempt to gain Carl's assistance in controlling Kong, he turns the prison cell's temperature down to zero, which puts both Jiro and Susan in a freezing environment. Carl refuses to help, even as his friends slowly begin to freeze to death. A while later, Dr. Hu enters the cell and states that Carl has been canceled. He then shackles Jiro to the wall and attempts to press Susan's face against the ice-covered metal walls. Fortunately, outside Kong has almost broken through the caged door and his banging begins to shake the entire lair. Hu and his minions leave the cell, and Jiro and Susan quickly make their getaway. Outside, Kong has crawled out of the underground lair and begins to flee. The great ape then dives into the frigid ocean and quickly swims away. Back inside, Jiro and Susan discover that Carl is still alive, but the three are once again captured and loaded onboard Dr. Hu's ship as the evil scientist sets sail in pursuit of Kong.
The ship soon arives in Japan, where King Kong has swum ashore. Dr. Hu plans to unleash his Mechani-Kong against its organic counterpart. However, Madame Piranha is hesitant to be a party to the inevitable collateral damage, and urges the doctor not to let the two monsters fight in Tokyo. After all, thousands would be killed. Dr. Hu ignores her sudden change in character as well as her pleas, and prepares his robot for combat. Down below, the submarine crew are chained in a cell, unable to help Kong. Suddenly, Madame Piranha enters and frees them, begging them to do their best to save the lives of the people in the city by leading Kong away before his mechanical doppelganger can engage him. The trio flee the ship and arrive safely in Tokyo, where the JSDF are preparing to fire on Kong. As Carl warns the army not to attack, Susan runs to Kong, whom picks her up gently. She calms him down and assures him that he will not be attacked. However, there is a loud crash behind them, and suddenly Mechani-Kong emerges through the remains of a destroyed building. Susan tries to warn Kong not to fight the machine, as it will most assuredly be a losing battle. Kong, however, carefully places Watson on the ground, and then turns to fight his robotic clone head-on. However, Mechani-Kong has been outfitted with the hypnosis device and, as Kong charges, the light, now attached to the top of the robot's head, begins to flash. Kong stops dead in his tracks and begins to slow down again. On the ground, Lt. Commander Nomura takes a shotgun and aims at the titular monster, eventually shooting and destroying the blinking light. Kong once again snaps out of it and finally charges to meet his opponent. The two seem evenly matched for a while, but Dr. Hu suddenly turns the tides of the battle and controls his robot to scoop up Susan. The giant mech then begins to ascend Tokyo Tower with Susan as his unwilling captive. Kong follows, and begins to climb after his foe. On the ship, Madame Piranha pulls a gun on Dr. Hu and threatens to shoot him. However, he triggers the silent alarm, and he and his minions quickly overpower her, leaving her with a bullet wound in her arm. Back in the city, the mouth of Mechani-Kong opens and the voice of Dr. Hu eminates from a speaker within. He warns Kong that if he does not return to the ship, the robot will drop Susan. Kong, however, continues to pursue his metal clone up the tower, and soon enough, the robotic ape lets go of its prisoner, sending Susan falling towards the ground. Kong catches her and sets her safely down on a platform within the tower, and then begins to climb after Mechani-Kong, finally able to fight it again. Below, Jiro climbs up the tower and rescues Susan. As the two monsters get higher and higher, the tower begins to shake more and more. Susan slips and nearly falls off the tower, but is saved by both Jiro and a team of policemen who bring them both safely to the ground. Back in the control room on Dr. Hu's ship, Madame Piranha decides to tip the balance in Kong's favor, and makes one last attempt to save the lives of the people of not only Japan, but of the world. The wounded traitor rises and quickly rips the wires and control cables from the wall. Dr. Hu turns and shoots her twice in the chest, and she falls dead to the floor. However, her actions, and her sacrifice, are not in vain, for outside, Mechani-Kong begins to short-circuit. Now disabled, the mechanical ape falls from the very top of Tokyo Tower and shatters upon impact with the ground. Having won the battle, King Kong beats his chest in triumph. The next day, Dr. Hu decides to beat a hasty retreat in his ship. However, on the dock, Carl Nelson, Jiro Nomura, and Susan Watson stand with King Kong. Susan commands Kong to "stop that ship!", and the ape obliges and dives into the sea in pursuit of the freighter. Kong soon catches the ship and begins to destroy it from the outside in. He pounds on it and begins to push it under. Inside, Dr. Hu is crushed by falling debris and is soon killed as the ship finally floods and sinks. With his job done, King Kong beats his chest and bellows in victory. He then turns and begins his long swim home to Mondo Island.
English VersionThe film opened in the United States in June 1968 on a double-bill with the Don Knotts comedy, The Shakiest Gun in the West. Contemporary American reviews were mixed. New York Times film critic, Vincent Canby gave it a particularly insulting review, calling Toho's Kong an "Uncle Tom," and commenting, "The Japanese... are all thumbs when it comes to making monster movies like 'King Kong Escapes.' The Toho moviemakers are quite good in building miniature sets, but much of the process photography—matching the miniatures with the full-scale shots—is just bad... the plotting is hopelessly primitive..."
The July 15, 1968 Film Bulletin, however, gave it a more positive review, saying "Grown-ups who like their entertainments on a comic-strip level will find this good fun and the Universal release (made in Japan) has plenty of ballyhoo angles to draw the school-free youngsters in large numbers..."