The film's structure relies on a massive pivot. Initially, the audience is led to believe the apocalypse is real. The twist is the "restoration" of the world the next morning. However, the true twist is that Alexander follows through with his vow despite the apparent safety.
He tricks his family into leaving for a walk, piles up furniture, and sets fire to his home. As the house burns, his family returns, trying to restrain him while he runs around in a manic state. An ambulance, summoned by the family, takes him away to an asylum. The film ends with the focus shifting to his son, who waters the dead tree, suggesting that the father's sacrifice has indeed secured a future for the next generation.