Oscar, a ten-year-old boy, is staying at a children's hospital. Neither the doctors nor his parents dare to tell him the truth about his illness. Only Rose, a woman with a grumpy attitude, who comes to deliver pizzas, communicates with him in a straightforward way. To distract him, Rose suggests that Oscar play a game: From now on, he should behave as though each day were the equivalent of ten years. She thus offers him an entire life in a few days. So that he'll open up even more, she suggests that he should also write to God. In his letters, Oscar talks about his suffering, worries, joys, falling in love for the first time, time passing by... A singular friendship develops between Oscar and Rose. Both have no idea how this closeness will affect their future lives.