Due to a malfunction in the fictitious Markt Ebersberg nuclear power plant near Schweinfurt, Bavaria, an MCA triggers a widespread evacuation and sends a panic through the region. Hannah, Paula Kalenberg, must look after her younger brother, Uli, while their mother is away in Schweinfurt for business. With no easy route home to Schlitz in East Hesse, Hannah agrees to ride with her classmate Lars and his friends. On the road, the teenagers catch fragments of radio news, but the true scale of the disaster remains unclear until they reach Schlitz, where Lars' mother pulls him from the car and declares that he cannot take them along because his family must flee.
Hannah, Paula Kalenberg continues on foot toward home, where Uli awaits. Their mother plans to join them later from Hamburg with the neighbors. Following emergency guidance to seek shelter, the siblings decide to wait in a cellar, hoping Elmar, a schoolmate Franz Dinda who had kissed Hannah before the alarm, will help them escape. But the mother rings to say they should flee to Bad Hersfeld with the neighbors, then take a train to Aunt Helga in Hamburg. With the neighbors fleeing and Elmar not yet appearing—he’s wrestling with the car keys and trying to start his parents’ vehicle—the children choose to bike to Bad Hersfeld anyway. Tragically, Uli is killed in a hit-and-run along the way, a blow that haunts Hannah throughout the ordeal.
A little later, a family with several children helps Hannah reach Bad Hersfeld station, where the father places Uli’s body in a nearby cornfield. Because the motorways are crowded and everyone is trying to flee by train, Hannah keeps an eye on the younger girls on the platform while the parents battle their way through. She briefly sees her friend Elmar again in the mass of travelers, but they cannot reach each other. Then the cloud burst hits, and Hannah collapses. She wakes in a hospital near Hamburg, where she befriends Ayşe, Claire Oelkers, a fellow patient coping with radiation symptoms, including hair loss. Elmar, Franz Dinda—also contaminated but coping—arrives later, finding Hannah in a fragile state.
A month later, Aunt Helga Gabriela Maria Schmeide comes to collect Hannah in Hamburg. Back at school, Hannah endures isolation due to visible radiation damage, especially her baldness, while Elmar remains by her side. Elmar’s family hopes to move to America, but he refuses, feeling he has little chance and opting to seek treatment instead. He even contemplates suicide, but Hannah intervenes in time. When Zone 3—the least-radiated area around Hannah’s hometown—is opened, the two travel there together, primarily to bury Uli in the cornfield. After the burial, they resume their journey toward Schlitz, and as they drive, Elmar notices a breeze on Hannah’s bald head, prompting her to lean out of the sunroof so her hair can fly freely in the wind.
