In the year 2020, cosmonaut Marcia (Faith Domergue) orbits the planet Venus while five 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. They discover signs of a lost civilization and an artifact indicating that the Venusians had looked human. But what of the strange singing sound they often have heard during their exploration? Do the anthropomorphic Venusians still exist?