To cheer Sophie up, Julien gives her a small tin box, a gift from his fatally ill mother. Because it is important to him, he asks her to lend it back to him from time to time. As Julien wants the box back at the moment he gave it to her, Sophie demands proof of how important it is to him. Julien disengages the handbrake of the bus without hesitation, and the bus full of children rolls down a hill. Their game has begun: the box changes its owner after each completed dare.