17-year-old Stella and her younger sisters, Luce and Aria, are locked inside their house with bars on the windows. Billions of people have died since sunlight has become too strong and now only men can go outside. Their claustrophobic life is brightened up by special games, such as the Air party or the Picnic by lake. But their father gets angry: he would like them to completely erase the past. Things break down when Luce, the second daughter, who is by now a teenager, starts asking about the outside...