Two boys who are apparently prone to various kinds of mischief find a spaceship in the woods and climb aboard only to find that the ship has autopilot and is programmed to return to the hostile planet of its origin. The film starts off with an astronomy lesson and the hostile planet turns out to be a hidden planet on the other side of the sun. Awaiting them there are two caped and antennaed young female cannibals and an enormous slow moving knife-headed creature named Guiron. Old favorite Gaos - or something that looks like him - makes a cameo but is defeated so quickly by Guiron that you will hardly notice him. Gamera to the rescue! Back home, the younger sister of one of the boys tries to convince her somewhat dour mother of what has happened, but she is told to stop making up stories and go study.
Indeed, this story is the sort of wandering, somewhat silly, and entirely fantastic thing that kids do make up. But that's exactly why it works. It's a kid film. It doesn't require expensive and fancy special effects, just a fun story, kids doing amazing things, and giant monsters.
I enjoyed this as a kid and enjoyed it again as an adult. The acting is passable for what it is - the younger sister is actually very convincing and sympathetic and the two boys do OK. The adults are presented entirely from a kid perspective (as was done in The Peanuts) - and are stereotypic and often over-dramatic). The cinematography is pretty good - again, for its purpose (this is not an art film nor even an adult action film). And the dubbing in the version I saw (Sandy Frank's name did not appear anywhere) was actually very good.
Fun little film - recommended!