César Petit, ten and a half years old, slightly overweight, lives in Paris with his parents. He envies Morgan Boulanger, his best friend, for his athletic ability as well as his maturity and popularity. César becomes interested in a pretty classmate named Sarah, but she seems to only have eyes for Morgan. Morgan finds out that his father, whom he’s never met, lives in England. Along with César and Sarah, he develops a plan for them to cross the English Channel without their respective parents’ knowledge, to find his father.