The French for 'tomboy' is 'garçon manqué', but that expression is probably avoided here as a title to avoid confusion with David Delrieux's film of the name made the previous year. Laure (Zoé Héran) is ten years ago and certainly makes a convincing boy. She has recently moved with her family – her unnamed parents and her younger sister Jeanne (Malonn Lévana) – to a flat in a new area. School has yet to begin, and this is very much a film in which children at play have a high profile.
On first meeting Lisa (Jeanne Disson) Laure says her name is Michaël, and is introduced to the other local children – all boys apart from Lisa – and is wholly accepted as a boy. Inevitably, despite this acceptance her days as a boy are numbered. The first hurdle is playing football for a time: her breasts undeveloped, she can remove her tee-shirt with no problem, but if she wants to go to the toilet she can't just go near the bushes at the edge of the pitch and stick out what she doesn't have to stick out. So she goes into the forest, but the boys call her (male, of course) name, she wets herself, and is of course laughed at.
Another ordeal is swimming, although she deals with that by putting a piece of plasticene between her legs. Then her sister Jeanne wants to see 'Michaël's' friends so she has to be sworn to secrecy. During the family evening meal Jeanne, when asked by her mother if she had a good time with Laure's friends, says she did, and that her favourite is Michaël: both girls laugh stupidly at this.
But time is closing in and Jeanne can't understand why Michaël's name isn't on the list of pupils attending the school lessons. There are only two weeks to go but in fact it's Laure herself who brings about the resolution of the problem: a boy pushes Jeanne, Laure hits him and his mother appears on the family doorstep with her son complaining about Michaël's behaviour. What Michaël? The secret's out and Laure is now seen as an oddity by her former friends.
This film, in its simple way, is making a very important point about difference, about the outsider trapped in a gender she (in this case) can't relate to. In 2019 Sciamma went on to win the Queer Palm at Cannes with Portrait de la jeune fille en feu, which was translated as Portrait of a Lady on Fire.