An atomic war has destroyed the earth and covered it with a "radioactive haze of death", except for a secluded desert valley that was protected by mountains and a strong wind. We see a guy, Tony, and a woman drive into the valley in their convertible, then two guys stumbling into the clear. They are Rick and Radik. Radik has been contaminated and may be dying. There's also a house inhabited by Louise and her father, who had prepared for this end of the world scenario. Louis is pining away for her boyfriend, Tommy, who didn't make it in time and is presumed dead. Soon, another survivor shows up, an old guy and his mule, Diablo.
Radik begins to get better, though he acts strange and goes out at night to hunt for game. He likes the raw meat. One day he kills a rabbit but a larger mutation shows up and scares him away. At this point we only see its taloned hand but when it is revealed, it's horrible looking, with multiple arms and three eyes. Louise's father wants her to marry Rick and start pumping out babies and she reluctantly agrees. However, she keeps on hearing a strange high-pitch noise and it's the ugly mutation trying to communicate. It's really her old boyfriend Tommy, transformed. There are scuffles between wise-guy Tony and Rick, since Tony wants to marry Lousie, and then between Tony and the father, who ends up shooting him.
The movie ends on an up note, with rain clearing away the radioactive haze and killing the mutants--and Rick and Louise leaving the valley to repopulate the planet.