Dr. Tom Anderson (Van Cleef), an embittered scientist, has made contact with a Venusian creature, while using his radio transmitter. The alien’s secret motivation is to take complete control of the Earth by enslaving humanity using mind control devices; the alien claims it only wants to bring peace to our troubled world by eliminating all emotions. Anderson agrees to help the creature and even intends to allow it to assimilate his wife (Garland) and friend Dr. Nelson (Graves). The Venusian then disrupts all electric power on Earth, including motor vehicles, leaving Dr. Nelson to resort to riding a bicycle.

After avoiding a flying bat-like creature which carries the mind control device, Dr. Nelson returns home to find his wife newly assimilated. She then attempts to force his own assimilation using another bat-creature in her possession, and he ends up being forced to kill her in self-defense. By then, the only people who are still free from the Venusian’s influence are Nelson, Anderson, Anderson’s wife and a group of army soldiers on station in the nearby woods.

Nelson finally persuades the paranoid Anderson that he has made a horrible mistake in blindly trusting the Venusian’s motives, allying himself with a creature bent on world domination. When they discover Tom’s wife has taken a rifle to the alien’s cave in order to kill it, they hurriedly follow her, but the creature kills Claire Anderson before the two doctors can rescue her. Finally, seeing the loss of everything he holds dear, Dr. Anderson viciously attacks the Venusian by holding a blowtorch to the creature’s face; Anderson dies at the alien’s hand as it expires.