Twelve-year-old Felix is allowed to spend the holidays at home alone for the first time, well taken care of by his parents' admonitions. It's a hot summer, and the whole city seems deserted. He feels as if he is the last person left in the world. Then he meets Uli, a girl his age whom he initially thinks is a boy. Together, they explore the empty houses in the neighborhood. During their adventures, they make a terrible discovery.