An expedition in the South Pacific lands on a tropical island where the natives worship the mysterious deity Gappa. An earthquake opens up an underground cavern and a baby reptile is discovered inside. The natives warn the foreigners to leave the hatching alone, but they don't listen and take it back to a zoo in Japan. Soon after, moma and papa Gappa start smashing Tokyo looking for their kidnapped child.

Tamio Kawachi
as Hiroshi Kurosaki

Yōko Yamamoto
as Itoko Koyanagi

Yuji Okada
as Daize Tonooka

Kōji Wada
as Mashida

Tatsuya Fuji
as George Inoue

Keisuke Inoue
as President Funazu

Zenji Yamada
as Captain of the Kamome-maru

Bumon Kahara
as Elder

Kōtarō Sugie
as Reporter #1

Saburo Hiromatsu
as Hosoda