Astronomer and scientist Ryoichi Shiraishi (Akihiko Shirata) is a troubled man, having recently broken off his engagement. Tonight he is at a local celebration near his village, but the festivities are abruptly stopped when the alarm about a huge forest fire is raised and three men perish in the flames while trying to extinguish them. One of Shiraishi's fellow scientists is Joji Atsumi (Kenji Sahara), who is intrigued by his research into the asteroid belt between the planets Mars and Jupiter which is believed to be the remains of the planet Mysteroid. But what connection does this investigation have with the disasters now befalling in Japan as Shiraishi's home village is swallowed up by a massive landslide, apparently taking him with it?
One of the many spectacular science fiction epics staged by the Japanese studio Toho, most of which fall in the shadow of Godzilla, The Mysterians (known as Chikyu Boeigun in its native land and the first of Toho's widescreen pictures) demonstrates the same appetite for destruction as the movies featuring that overgrown, firebreathing lizard. Scripted by Takeshi Kimura, it even has its own giant monster, the third disaster to curse the country, in the shape of a towering robot mole which, in truth, looks more like a giant, metal chicken but which nevertheless has to be repelled by the ever-present military as it goes on a rampage.
Someone, as Atsumi's superiors (including the familiar Takashi Shimura as the head boffin) correctly surmise, has to be behind all this and the fingers of blame are quickly pointed in the direction of the Mysterians of the title. This fantastical explanation is so readily accepted that it's almost as if the authorities are used to this sort of behaviour by now, as even this early in the cycle of such films the conventions are set in stone. It's not long before a delegation of the space aliens make contact and actually expect us to believe that their intentions are peaceful after all that wanton mayhem they've caused. Naturally, we Earthlings are sceptical.
The Mysterians are a brightly coloured bunch, looking like a cross between humanoids and ants with their large helmets and almost as large dark glasses, and their proposals are simple. They want a two mile area of Japan to live on - oh, and did they mention they need Earth women for breeding purposes? A mere trifle, they think, but we're not going to hand over our females to just anybody and outrage followed by an all out war is the consequence, with the aliens proving to have the upper hand. You know what this means, don't you? The callous destruction of meticulously assembled miniatures, that's what, and a lot of it too.
The characters don't simply put their faith in firepower, they put great trust in science even as that new-fangled technology is used against them, including the welcome sight in the sky of that nineteen-fifties obsession, flying saucers. So when everything is thrown at the Mysterians to little effect, and then they have the audacity to start kidnapping women, that's the last straw and now we use our secret weapon. In the meantime, Shiraishi has appeared on television to plead for Earth to let the aliens have their own way, and Atsumi mounts a one man campaign to release the captives before everything goes boom. The story tends to become bogged down with the action and neglects the human element, but there's plenty to keep the eyes occupied and the mixture of a "science with responsibility" message with practically non-stop special effects is an appealing one. Music by Akira Ifukube.