 In the year 2020, cosmonaut Marcia (Faith Domergue) orbits the planet Venus while two astronauts and a robot journey on the surface. Professor Hartman (Basil Rathbone) is also on hand to observe the exploration from a distance. The explorers are attacked by prehistoric beasts, and then lose their robot (and nearly their lives!) in a volcanic eruption that engulfs the planet. They conclude that the Venusians were really human beings who destroyed their civilization with nuclear warfare.