An expedition goes out to a remote island to find a priceless opal. This opal happens to be the egg of the powerful Barugon, a huge lizard-like monster that can freeze foes with its long tongue or disintegrate them with its devastating rainbow ray. When Gammera begins to fight Barugon, several plans begin to stop both monsters and keep the damage of Japan at a minimum.
| Actor | Role |
|---|---|
 Ted RusoffKeisuke Hirata (voice) | Keisuke Hirata (voice) |
| SSilvia FaverKaren (voice) | Karen (voice) |
| RRobert SommerOnodera (voice) | Onodera (voice) |
 Robert SpaffordIchiro Hirata (voice) | Ichiro Hirata (voice) |
| FFrazier RippyDr. Matsushita (voice) | Dr. Matsushita (voice) |
| CCarolyn De FonsecaSadae Hirata (voice) | Sadae Hirata (voice) |
| AAnthony La PennaNarrator | Narrator |
 Kōjirō HongōKeisuke Hirata | Keisuke Hirata |
 Kyōko EnamiKaren | Karen |
 Yūzō HayakawaKawajiri | Kawajiri |
 Takuya FujiokaDr. Sato | Dr. Sato |