Betty Boop campaigns for Grampy to be the new mayor and he wins. As soon as he takes office, the citizens come out from everywhere to complain and to demand he fix things. Grampy is in his element.

Gaira, a humanoid sea beast spawned from the discarded cells of Frankenstein’s monster, attacks the shores of Tokyo. While the Japanese military prepares to take action, Gaira’s Gargantua brother, Sanda, descends from the mountains to defend his kin. A battle between good and evil ensues, leaving brothers divided and a city in ruins.