Hirata (Kojiro Hongo) and Onodera (Koji Fujiyama) head to New Guinea to retrieve a massive opal hidden during the war. They head into a scorpion filled cave despite the warnings of native girl Karen (Kyoko Enami) and indeed find the huge gem. However, Onodera decides he doesn't want to share anymore and tries to kill Hirata. He heads to Japan on his own. But the opal actually isn't, it is an egg. It hatches in Japan, the huge monster Barugon begins to wreck the usual kind of havoc.
Gamera is attracted by the mayhem and fights Barugon though is defeated by it's freeze ray. Hirata and Karen are now in Japan and help the military with various schemes to try and defeat Barugon, despite the treachery of Onodera. The schemes fall short but Gamera is revived just in time to fight Barugon in an epic final battle.
This is the usual Japanese monster movie fare, plenty of destruction, plenty of waddling monsters destroying buildings and tanks. Barugon's rainbow ray is a rather lovely effect. The jungle scenes and Onodea's antics add a bit more interest beyond the usual monster battles.
