Ewen has a secret that he has kept from everyone and nobody knows about it. He goes out at night in the streets of Paris, which would worry any parent of a young boy. But Ewen doesn't live at home with his mother and father. He lives in a hospital because he has cancer. And his cancer doesn't keep him from going out on adventures. When a boy named Benjamin is hospitalized for the same reason in the same hospital, Ewen and Benjamin become friends. After a time, Ewen decides he can trust Benjamin and reveals his secret to him. Unbeknownst to everybody, they join forces to escape at night and fulfill exciting adventures outside the hospital. Only Alcibiades, a mean and terrible man who doesn't want to share his territory, is aware of their nocturnal escapades. And Alcibiades has something to say about it!