In 2020, after the colonization of the moon, the spaceships Vega, Sirius and Capella are launched from Lunar Station 7. They are to explore Venus under the command of Professor Hartman, but an asteroid collides and explodes Capella. The leader ship Vega stays orbiting and sends the astronauts Kern and Sherman with the robot John to the surface of Venus, but they have problems with communication with Dr. Marsha Evans in Vega.

A dull office worker transforms into a costumed peeping tom at night.

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.