During a visit to a friend at the Robert Debré pediatric hospital in Paris, Momo, an actor in need of roles, meets Michel, the director of an association of volunteer clowns, who visits the hospitalized children. Thanks to Michel's encouragement and confidence, Momo is convinced to play a role in the lives of these children. His challenge: to make them laugh despite the illness. Very quickly, the children fall under his cartoonish charm and Momo becomes an integral part of the pediatric ward. With the complicity of Michel his mentor and Bénédicte, a nurse from the hospital, Momo will have the idea of staging a circus show within the hospital in which each child will have a decisive role.