Ako (Nobuhiro Kajima) and Tomoko (Miyuki Akiyama) chance upon a landed flying saucer and naturally, being small boys, go on board. The saucer takes off and goes into space. Aliens kidnap the boys to find out what is in their brains, and if they don't find anything interesting they'll eat their brains instead.
Gamera heads into space to rescue the boys and has to fight the monster Giron who has a gigantic knife sticking out of his nose...
So, this is quite an odd film and definitely aimed at children. The plot is nonsense and it includes the usual destruction of model buildings by people in monster suits. Giron with his big knife is an interesting foe for Gamera for sure and pretty menacing too.