Marie-Luce Bison, 14 years old, is raised by her father in a cheerful boarding house for seniors where he is the director. It is soon the costume party of her new college: her father does not want her to go ... and anyway, she is not invited. But pushed by Albert, her 80-year-old best friend, Marie-Luce crashes the party, dressed as a man. That evening, everyone takes her for a boy... a boy who is looked at and who pleases. She then decides to invent a male double named Leo to finally live her teenage life. Of course, at home, the relationship with her father becomes complicated.