It begins as a typical morning in the Wetherly household, where Carol is busy getting her three children, Brad (the eldest), Mary Liz, and Scottie, prepared for school. Her husband, Tom, and Brad share a quick bike ride, during which Tom's criticism of Brad becomes apparent when the young boy struggles to conquer a steep hill. On their way back, they greet Henry Abhart, their elderly neighbor, and Mike, the gas station owner, who has a special needs son named Hiroshi, often seen fishing with the Wetherlys.
As Carol immerses herself in directing a play titled The Pied Piper of Hamelin at the elementary school, the children eagerly participate. Mary Liz accompanies the performance on piano, while Scottie takes on the role of a small crippled boy.
That night, insomnia plagues Carol as she worries about what to give Brad for his upcoming thirteenth birthday, while Tom sleepily reassures her the event is still two months away. This prompts Carol to consider starting a diary to document their lives as her children grow.
The following afternoon, while the children enjoy television in the living room, Carol sifts through incoming messages on their answering machine. Her mother checks in from Chicago, but Tom, who is in San Francisco for business, leaves conflicting messages about returning home. Just as the kids are trying to adjust the fuzzy TV picture, breaking news interrupts their broadcast with urgent warnings: bombs are dropping across the eastern U.S. and in locations near San Francisco. Citizens are urged to keep telephone lines clear for official communication. When the television suddenly goes dark and alarms begin blaring, Carol urgently calls for her children to take cover and shield their eyes.
Once the chaos subsides, the community slowly emerges from their homes in a state of confusion. There’s a chilling atmosphere as many gather at Henry's home to seek updates, but communication with cities that have been attacked is scarce. Henry, a licensed ham radio operator, assures his worried neighbors that although they may be down, they are not out. He offers his supplies, stating, "If anyone needs food or water, the Abharts will share what they have." Carol, in her desperate search for her husband, takes in Larry, a neighbor's boy left alone after his parents go missing.
As days turn into a grim reality, a community meeting reveals little optimism. Amid looting and radiation fears, everyone is left to ration essentials. Carol’s worries deepen when neighbors begin to fall ill, and radiology assessments confirm they are facing increased exposure to dangers. Despite these ominous signs, life persists; the children give their much-anticipated play, and Mary Liz continues piano lessons with Henry's wife.
Tragedy strikes when the Pitkins face the loss of their baby, leading them to leave for a supposed safer place, leaving Carol hopeful for their return. The tension heightens as Scottie becomes gravely ill, and despite Carol’s frantic search for his teddy bear, he succumbs to the illness.
As despair grips the community, the toll of loss unfolds. Larry and Mary Liz both pass away, leaving a sense of desolation. Amid this bleakness, a desperate confrontation occurs when the boy who stole batteries breaks into the Wetherly home, prompting Brad to defend their space while losing his bike. With their resources dwindling, a third community meeting sees more empty chairs than attendees. Even the police chief is near his breaking point, persisting in their limited duties despite the pervasive suffering.
With signs of radiation poisoning manifesting in Carol, the news of Henry's death devastates her. In her grief, Carol finds a moment of connection with Rev. Hollis, yet the weight of their reality remains heavy. Ultimately, Carol and Brad resolve to take their own lives, taking Hiroshi with them. In a moment of shared despair, they contemplate this choice in their car, but the impulse to continue living resurfaces. On what should be a celebratory birthday, Carol offers a small treat with graham crackers and jam lit by candles, while Hiroshi unexpectedly finds and presents Scottie’s cherished teddy bear, bringing a glimmer of joy amidst their grim circumstances. Though their fate is sealed, a profound sense of peace envelops them in that moment.
