In contemporary France, a nuclear war breaks out over Europe, and a group of visitors to a local chateau take cover in the basement. When they venture outside after the fighting stops, they discover that the chateau has sustained serious damage and the surrounding lands have been laid to waste. The survivors try to rebuild the house as best they can, and they begin growing food in order to sustain themselves, until they encounter Fulbert (Jean-Louis Trintignant), a deranged fascist who is leading a band of ragged survivors who live in several abandoned railroad cars. The survivors of the chateau defeat Fulbert, and his forces join with the people of the chateau to build a new society. However, they are soon ambushed by government troops, who are rounding up survivors of the nuclear attack and relocating them to concentration camps. Three of the chateau survivors are able to escape and attempt to make their way to safety.