A giant monster resembling a bat is awakened and threatens to destroy all of Japan until Gamera comes along and decides that is not so hot of an idea.
Gamera and earth scientists work together to get rid of the threat. Gyaos is a very interesting monster in that he eats people, has a laser ray that can slice thru anything and he cannot stand the sunlight. As in the first film there is a child who has a link to Gamera.
These films are squarely aimed at children, yet there is enough monster mayhem to keep any adult monster fan happy as well. This was turned out on VD by Shout Factory on a double bill with "Gamera Vs. Viras" and both films have their English language version as well as the original Japanese language version.
If you like giant monsters you'll like this film.