Godzilla vs. Monster Zero is the sixth Johnson Studios remake.
At the outset of the movie, the two-man spacecraft (on an off-record mission in order to make the Space Race more spectacular), crewed by one Japanese and one American (Fuji and Glenn), is approaching Jupiter to visit the newly-discovered "Planet X", which inexplicably maintains a position directly behind Jupiter. The planet is rather dark, but still lit up enough to be visible and for it to be possible to navigate its surface. The spacecraft lands, and the astronauts disembark.
One astronaut vanishes, and the other wonders where he, and the spacecraft, have gone, and then a flat voice intones to him, instructing him where to go. The astronauts are led through subterranean corridors to the office of the Controller of Planet X.
The spacecraft is safe, he assures them, and indicates that they are about to be attacked. The astronauts recognize the attacking creature, King Ghidorah. After a brief black-out, when the astronauts are cut off from being able to see and hear the Controller, they are assured that the monster, known as Monster Zero, has left.
The Controller says that they want Earth's help: to be allowed to capture Monsters Zero One, Zero Two, and Zero Three, known to Earthmen as Godzilla, Rodan, and Anguirus. In return, Planet X will gift humanity with a wonder drug that cures all diseases. The astronauts agree to return to Earth with the proposal. As they lift off, they say on the radio to the Controller, "We're glad we found friends on Planet X."
Meanwhile, Fuji's sister has a boyfriend, Tetsuo, who's invented a personal alarm he thinks women could use to summon assistance if they're endangered. It creates a horrific loud noise that can be heard blocks away, and wonders why nobody's interested in buying it, but then a Miss Namikawa comes and makes an offer to buy it as an educational device, but keeps putting Tetsuo off on completing the deal.
Fuji and Glenn arrive home, and tell their superiors of the offer by Planet X. Scientists begin searching for Monster Island. Then, the Controller of Planet X makes mysterious appearances on Earth, and Glenn becomes suspicious about Planet X. The Controller finally makes his appearance overt, "apologizes" for his unannounced presence, and offers to help locate the two monsters. Three Planet X spacecraft rapidly fly off and extract the three monsters from Monster Island, revealing its location and leaving Varan, Manda and Baragon quite angry at being left behind, while Mothra simply states (via Tom Stevenson's translator) "This isn't our fight. It's there's".
Glenn, Fuji and one of their superiors are invited aboard a spacecraft to accompany the Controller back to Planet X, a trip that takes only a few hours; the Controller says that soon they'll be able to travel as fast as light. On reaching Planet X, there is almost immediately an attack by King Ghidorah, and the thre from Earth are released to battle it. King Ghidorah is driven off, Godzilla dances his now-infamous victory jig, and the Controller exults about that. He presents a box that, he says, contains information about the miracle drug, and presents the three men with a faithful duplicate of their spaceship so they can fly home.
On arrival, the box is taken to a special international meeting and is opened to find a reel-to-reel tape. It is loaded onto a machine and set up to play. When the speakers remain silent for a long period, some wonder if the systems are compatible, but others say their system is exactly the same as ours. Finally, there is a beep, and the voice begins. "This is the Controller of Planet X. You will listen to my instructions..." It is an ultimatum to surrender to Planet X. Their motive: they want Earth's water, land, minerals, and (since the aleins are so anatomically similar to humans) women. All men will be forced to work until they die, and all children will be eaten. Alive.
The aliens arrive, destroy the spacecraft, and threaten to release the four creatures, which are now all under Planet X's control. In a show of confidence, the aliens even betray the method of control: magnetic waves. The Earth scientists realize that they could exploit this information, and work rapidly to find a way to disrupt those magnetic waves, while in the meantime, Earth's armies fight nearly in futility with conventional weapons as the monsters wage most of their destruction against Tokyo (Godzilla), Sidney (Rodan), Shanghai (Anguirus), and San Francisco (Ghidorah). The remaining monsters on Monster Island, meanwhile, head off to combat the aliens' war machines, which are all Mogueras. The Controller reveals their alliance with the Mysterians, and the Mysterians send their own message promising revenge for what transpired in 1957.
Tetsuo, meanwhile, is dissatisfied with the lack of progress on his device, and his inability to get Miss Namikawa to tell him what's happening. He gets imprisoned by the Planet X soldiers. When Glenn, who was infatuated with Miss Namikawa, is also arrested after finding out something about her - she's from Planet X and all their women are virtually identical, he and Tetsuo put clues together. Namikawa gave Glenn, before she was disintegrated by a Planet X soldier, a letter, and in it she says that one simple sound will destroy the people of Planet X. It is the sound made by Tetsuo's "lady beware alarm". He still has the prototype, takes it out and sets it off. It upsets and paralyzes the Planet X soldiers and Glenn can immobilize them and they escape.
They reach the space center scientists and explain about the device. Arrangements are made to broadcast it on all radio and television stations, a tactic that will be employed when the magnetic disruption devices are deployed.
The four monsters are removed from Planet X control, as Planet X spacecraft explode and personnel escape the noise by blowing up ships. Planet X withdraws its attempts to conquer Earth. Meanwhile, Godzilla, feeling used and remembering King Ghidorah, attacks King Ghidorah near Tokyo with the aid of Anguirus and Rodan, forcing King Ghidorah into a retreat. The last of the Mogueras are also destroyed, and Baragon and Varan begin tossing the head of one back and forth as if it were a ball.
Glenn and Fuji are to be sent to Planet X again as ambassadors to seek peaceful relations, which is mentioned as never happening, as the two astronauts are forced to return to Earth empty-handed after what they describe as a "space chicken with hooks for hands and a buzzsaw in its abdomen" chases them off. Meanwhile, UN Secretary-General U Thant proposes a unified organization to defend against further alien invasions and hostile kaiju.
Differences from Original
- The original home video and TV title is used
- Anguirus is added to the fray, and given the designation Zero Three
- Gigan makes a cameo at the end, but is not named