Simon is 7 years old. His mother Susan, with her puppet shows, university classes and her two children she is raising alone, hasn't got a minute to herself. Song Fang is Simon’s babysitter, she is taiwanese and studies cinema at Paris. On his way home from school, Song Fang leads him through the streets and cafés of his neighborhood, teaches him to play flipper… Simon has another friend too, a strange presence that follows him everywhere : a red balloon flying over the roofs of Paris...