Roseanne Rogers, Susan Douglas, trudges from place to place, searching for another living human being as a stark headline from a nearby newspaper warns that detonating a new kind of atomic bomb could push humanity toward extinction. Her journey leads her to her aunt’s isolated hillside house, where she faints upon discovering Michael, William Phipps, already living there. Initially, she is too numb to speak and slow to recover, but she gathers the courage to resist an attempted sexual assault and, in a quiet moment of honesty, reveals that she is married and pregnant.
Two more survivors arrive in a car, drawn by the smoke curling from the house’s chimney. Oliver P. Barnstaple, Earl Lee, an elderly bank clerk who clings to denial, acts as if he’s simply on vacation, while Charles, a thoughtful and affable African American man, Charles Lampkin, explains their survival: they were locked inside a bank vault when the catastrophe struck, or sheltered in a lead-lined X-ray room. Roseanne had been in a hospital’s lead-lined X-ray room, and Michael had been trapped in an elevator in New York’s Empire State Building.
Barnstaple grows sick, and Michael suspects radiation poisoning, though Barnstaple eventually seems to recover and longs to see the sea. The group soon drags a man named Eric, James Anderson, out of the ocean. A mountain climber, he recounts how a blizzard trapped him on Mount Everest and how he crawled down to base camp only to find everyone dead, then wandered across Asia and Europe to the sea, where more bodies lay. He eventually reached Hawaii by ship, finding only more corpses, and a plane ride home ends in fuel exhaustion near the United States. In the end, Barnstaple dies peacefully on the beach.
The next day, Charles helps Michael with a construction project, and Michael watches Roseanne bring food to the injured Eric. Michael suspects that Eric is exaggerating his condition and questions whether Roseanne should be running about for him. Eric’s presence quickly becomes divisive; he sows discord and theorizes that they are somehow immune to radiation, pushing the group to search for other survivors. Michael remains skeptical and warns that radiation will be most concentrated in the cities Eric wants to scour.
Eric also reveals a racist streak and clashes with Charles, who objects to his views. A confrontation erupts, and it stops only when Roseanne goes into labor; she delivers a boy with Michael acting as midwife. Afterward, while the others labor to build a new life, Eric retreats to his own space. He then vandalizes the group’s cultivated field by driving a jeep through it, destroying part of their crops. Michael orders him to leave, but Eric pulls a pistol and declares he will depart only on his own terms.
One night, Eric confides that he plans to head to the city, Oak Ridge. Hoping to learn what happened to her husband, Roseanne agrees to accompany him, though he insists she not tell Michael. After stealing supplies, Eric is challenged by Charles; a struggle ends with Charles being stabbed in the back and dying.
When they reach the city, Eric begins looting, while Roseanne seeks out her husband’s office and then his hospital waiting room. There she discovers his remains and longs to return to Michael, but Eric refuses to let her go. A struggle exposes Eric’s advanced radiation poisoning, and he runs away in despair.
Roseanne starts the long walk back to the hillside house, only to lose her baby along the way. Michael, who has been searching, eventually finds her. They bury their son and return to the house, where Michael quietly resumes tending the soil and Roseanne joins him, steady and resolute in the quiet life they cling to together.
