Dr. Douglas Martin (Peter Graves) is a nuclear scientist working on atomic bomb tests. While collecting aerial data on a United States Air Force (USAF) atomic blast at Soledad Flats, he loses control of his aircraft and crashes. He appears to have survived, unhurt, walking back to the air base with no memory of what happened. On his chest is a strange scar that was not there before the crash.
When a plague devastated life on Earth, the population died or became a sort of zombie living in the dark. Dr. Robert Morgan is the unique healthy survivor on the planet, having a routine life for his own survival: he kills the night creatures along the day and maintains the safety of his house, to be protected along the night.
He misses his beloved wife and daughter, consumed by the outbreak, and he fights against his loneliness to maintain mentally sane. When Dr. Morgan finds the contaminated Ruth Collins, he uses his blood to heal her and he becomes the last hope on Earth to help the other contaminated survivors. But the order of this new society is scary.