At the initiative of Nath, an environmental activist and Laurent's girlfriend, the group of friends Thomas, Laurent, Marc and Aude, will embark on a punitive expedition to a cosmetics laboratory. A series of incidents will cause an inexplicable phenomenon, a lightning bolt that strikes Thomas and causes a strange burn on his arm. And the next day, Thomas, stunned, wakes up transformed into a girl... Justin, his little brother, and Aude, his best friend, will be in on the secret and help Thomas hide this strange phenomenon.

Thomas, very disturbed by what happened to him, realizes that his transformation can be caused by a shock to his scar. He dreads going back to school more than anything, and will try to escape it by pretending to be sick, which is also contagious. Aude accompanies him to the doctor, but Thomas runs away and prefers to continue to hide everything, even if he gets a little tangled up in all his lies.

Finally back at high school, Thomas falls head over heels in love with Ally, a senior. His friends will overwhelm him with good advice on how to seduce her. So he will try his best to meet her, but he must also learn with Aude to master his new girly appearance, the all-important problems of clothes and makeup. And apparently, his "girl" version is more successful than his "boy" version. But with Ally, it's not a given this time.

Determined to make some pocket money, Thomas is forced to transform himself into a girl to get a babysitting job. He will discover that it is not so easy to look after a little pest named Lola, and to manage a baby's diapers. Fortunately, friends are there, and Aude, who had lost the diary where Thomas's whole story was told, will end up finding him where no one expected...

Faced with Thomas' disastrous school results, and the fact that they caught him dressed as a girl, his parents decide that he absolutely must see a shrink, who is also a shrink. She will not bear the revelation, and the parents will conclude that it is a classic teenage crisis.

Emmanuelle, having unwittingly saved Ally's grandmother's bag, will have to complete her civil status to face a notoriety that she would have gladly done without. Thomas will have a hard time destroying his image, and becoming happy and hidden again...

Aude only has eyes for Bastien, the football player. But Bastien only has eyes for Emmanuelle, who must learn how girls get rid of boys they don't want. And to top it all off, Nath is jealous of the female football players and forces Laurent to follow a draconian diet.

Thomas, more and more in love with Ally, will use Emmanuelle's appearance to join his girls' club, all fans of the series "Spy Witches". Aude tries in vain to oppose it. Thomas' attempts to attract Ally's good graces will end in a rather catastrophic way, but will have done Justin a good service.

Thomas, who accompanies Aude to a casting for singers, unwittingly transforms into Emmanuelle, and the two girls are selected for the final. But Aude falls ill, and Emmanuelle does not want to give up on running, which Aude experiences as a betrayal. The group must come to the aid of Nath, who is disturbed by the birth of her little brother.

Laurent has a brilliant idea: the group is going to do a reality TV show. Thomas falls heavily and breaks his arm. Surprise! The shock does not cause any transformation, and the process seems to have disappeared for good. After the joy of this realization, Thomas will miss Emmanuelle, especially since he could have won the young female writers' competition.

Thomas is furious to receive an English correspondent, who turns out to be a girl. Faced with the perfect understanding between Karen, his correspondent, and Aude, Thomas will take on the appearance of Emmanuelle to share the girls' little secrets. And he will discover that he is much more attractive than he thought.

Thomas is almost jealous of Emmanuelle's popularity. Noticing that his friends have just forgotten to wish him a happy birthday, he decides to participate in the weekend planned in Chamrousse in his female form, and to make her odious to everyone. But Emmanuelle, faced with Luc's suspicions about her true identity, will, once again, owe her salvation to Aude.

Marc, Thomas' best friend, is in love with Emmanuelle. Thomas is devastated. In addition, Thomas' parents and the high school principal are starting to think that this weird Emmanuelle is going too far. Life is becoming more and more difficult for Thomas. He will confess the truth to Marc, and make a desperate attempt to get rid of this decidedly too cumbersome female double once and for all. Fortunately, Marc, Aude and Justin are there...

Thomas offered Ally, for her birthday, a day in a beauty salon. And of course, by transforming into Emmanuelle (his female double), he will accompany Ally. The dream! However, a major problem arises: Thomas can no longer transform into Emmanuelle!!! A genetic “bug” assures Justin, his little brother who has decided to help him. Over the course of attempts to stabilize his crazy metabolism, Thomas undergoes increasingly bizarre transformations, until he transforms into his own mother!!! Fortunately, this last transformation allows him to discover his mother's plan, to send him to boarding school.

Thomas sees another “troublesome” year looming between his absences from school and the appearances of his female double. So he decides to solve the problem once and for all by creating fake parents for Julia! With Marc’s help, this crazy project gradually sees the light of day: first of all thanks to an unemployed actor ready to play Julia’s father, whom the two friends recruit through a classified ad, then, thanks to Aude’s cousin, who lives in Marseille, but who, following sentimental and financial setbacks, is currently squatting in Aude’s room...

Nothing is going well at home. Indeed, for the first time in his life, Justin is in love. Her name is Marie and she is crazy about extreme sports. Thomas decides to help Justin because he is his little brother, and especially because he negotiated 318 rounds of washing up if the operation "Make Marie fall into Justin's arms" is successful...

In two days, it's the "En avant la Sic-Mu" festival! Thomas brings everyone into the adventure. Writing the lyrics, composing the music, rehearsing, it's a total blast between the girls and the boys. Until Marc and Laurent bring back Nath and Aude's stage costumes. Mini-skirts and ultra-low-cut tops! It's a clash. Out of the question for the girls to play the "Barbie-potiches"! Since that's how it is, they'll both sing. The war of the sexes has been declared! Even Thomas can't stop it and has to run from one group to another.

Thomas and Julia learn at his own expense that girls are sometimes mistreated. He decides to campaign in a feminist association and goes there in Julia. What a surprise to discover that his mother is part of this association and never stops complaining about three men who are poisoning her life. Thomas concludes that his mother is talking about Justin, his father and himself who are supposedly the worst machos! War council among the men of the family who decide to make an effort before it is too late...

Aude is on the verge of a nervous breakdown... Between her henpecked father and her psychorigid mother, she's suffocating! So when she sees Cédric for the first time on his motorbike, hair blowing in the wind... she completely cracks. He's her great breath of freedom! Like a hurricane, love carries them both away! For Cédric, Aude would do anything...

Laurent is starting a new business: he has decided to shoot a horror film that he will then sell online. Thomas' parents' chalet, a remote place in the mountains, would be the ideal setting. The problem is that they don't want to hear about it. It doesn't matter, the film will be shot in the apartment of Yann, a new friend, who knows everything, who has seen everything, and who annoys Thomas to the highest degree...

Nath is, once again, exasperated by the guys. She has just been kicked off the men's hockey team that Marc and Laurent are on. With Aude, she decides to create her own women's ice hockey team and face the boys' team. They have a week to learn everything! The girls start recruiting a few friends and Aude enlists, almost by force, Thomas as Julia (still as motivated to play sports...). The beginnings are more than difficult and the training sessions are a real disaster, because the girls don't even know the rules, as for adjusting the equipment... we don't even talk about it... Fortunately for the girls' team, Thomas' paternal grandfather, Artémus, a colorful adventurer, who has arrived for the week, decides to take them under his wing... To lead them to victory and given the level of the girls, all tricks, even the most devious, are now allowed...

Out of male solidarity and… also for a compilation of 15 CDs, Thomas agrees to play Julia as Marc's girlfriend to dispel any illusions for Joséphine, the daughter of Marc's father's boss, who has organized a party. Marc's plan works wonderfully, even a little too well because Joséphine quickly takes refuge in her room. Julia, feeling guilty, discovers a girl who is really uncomfortable in her own skin, hyper aggressive. Using everything he has learned since he transformed into a girl, Thomas will try to restore Joséphine's confidence in both Julia and a boy. But Joséphine quickly falls in love with Thomas. How can he get out of this mess without hurting Joséphine? Thomas sees only one solution, make believe that Thomas is going out with Julia! Fortunately, thanks to this double betrayal, Joséphine will surpass herself and prove, during a bowling tournament organized by the gang for the rescue of Ursule, Nath's grandmother's tarantula, that she is worth much more than everyone believes.

Thomas's birthday is coming up. He's panicking at the idea of ​​having his first party, especially since everyone is ready to give their opinion.

Thomas has decided to invite Ally to his party through Julia so as not to be refused. But before doing so, he has a strange dream where he can no longer transform into a girl and where his female double has become independent to lead her own life. Thomas finally feels free, but this Julia blames him for what he did to her when she was his double and is determined to get revenge for past humiliations. When she proves capable of transforming into Thomas, the dream turns into a nightmare! Two Thomases begin to haunt the schools in the hallway. What if Julia took advantage of this power to steal Thomas's birthday party? What a relief when he wakes up to discover that it was all just a dream! But maybe Thomas will now think twice before using his double indiscriminately.

Thomas and Marc have been trying to flirt online for weeks, much to the dismay of Thomas' parents who have discovered a monstrous phone bill that they are demanding he pay. While Thomas is forced to "save up" for the first time in his life, the two friends get a date with a beautiful 25-year-old woman, Maryline, a casting director. Marc falls in love at first sight, but is far too shy to try anything, so he persuades Thomas to go as Julia to discover Maryline's tastes. Still unable to manage the timing of his transformations, Thomas is noticed by Maryline. Under her spell, Thomas even agrees to overcome his fear of heights and bungee jump for an advert. But when Marc learns that Thomas lied to him and ends up going out with Maryline, the two friends argue... Will Thomas' betrayal mark the end of their friendship? Thanks to Julia, will Thomas be able to be forgiven?

Thomas saw an ad for a dance competition exclusively for non-professional dancers. It's the perfect opportunity to make his dream come true: to dance! However, he doesn't dare, for fear that his friends will make fun of him. But when he discovers that Ally has also signed up for the competition, he decides to sign up, but discreetly, as Julia! Ally and Julia will quickly become the two favorite dancers in the competition. But only one will be chosen! For Ally, this competition is her whole life; which puts Thomas in a dilemma: between his love for Ally and his desire to win the competition even as Julia, what will he choose?

For their part, Laurent, Marc and Justin organize a small trafficking of fetish objects of girls from school. When they decide to take it to the next level and film the girls' locker room, they discover that Ally may not be who she claims to be... Will they succeed in stopping Thomas from abandoning his dream for a girl who manipulates him?

Thomas has promised to organize New Year's Eve. He's in a panic and doesn't take the time to listen to Aude who tells him that she won't be at the party. Thomas, furious, pushes the boys to go flirting on the ski slopes in order to find girls for New Year's Eve. When Aude and Nath, feeling guilty, decide to join them in the snow, they get upset. Nath breaks up with Laurent and Aude makes Thomas understand that he is nothing but a dirty egoist. To make up for his mistakes and try to repair Nath and Laurent's relationship, Thomas will transform into Julia to flirt with Laurent, while Marc will flirt with Nath on his side: which will make them understand that they still love each other. Unfortunately his plan turns into a disaster. New Year's Eve seems definitively abandoned especially when Thomas discovers what Aude has to undergo cosmetic surgery. Will Thomas manage to save New Year's Eve and prevent Aude from doing something stupid while revealing his true feelings to her?