It’s September 1963, and Voltaire High is getting ready for another school year. For the first time ever, this establishment will welcome girls: 11 of them to be exact, all freshmen. If the Principal is delighted with this experience, Vice-Principal Bellanger isn’t convinced. He and his wife Jeanne, the school nurse, will soon have to deal with the unforeseen excesses of coeducation.

Big day for Freshman Class 1: it’s their first Physical Education class, with its share of surprises for the girls. And it’s the class president election… It is also a trying day for Bellanger: it’s the day of his nephew’s disciplinary board hearing, and he needs to keep a close eye on the trials and tribulations of Miss Couret, the new English teacher, who is trying to fit in.

This week, the students will be pairing up to do an exposé. Simone is glad to see Jean-Pierre when working at Michèle’s, who hopes to finally get a good grade. Annick meets her mum’s new boyfriend, but is wary of him. The student-teacher soccer game is coming up, breaking with tradition this year as Bellanger is a referee and there is a woman on the field!

Bellanger is excited to be back in at school again after the Christmas break… But today, the boys are restless. It infuriates Michèle, who’d like to know what "makes you blind" and can’t stand being treated like a little girl. When the source of all this commotion is revealed in the middle of English class, Couret and Bellanger have to team up to deal with this disciplinary issue together.

Tonight, Jeanne, the school nurse, goes to the theater with Denise. There, she meets Irène, an actress who deeply moves her. On her way back, Denise crosses paths with Bellanger, who walks her home and confides in her about his love life. Meanwhile at the Courets’, they’re having a hard time understanding Camille’s sudden change in life: everything was going really well between her and Francis…

Annick is disgusted by the upcoming frog dissection, and suggests stealing the batrachians, in exchange for 1h of tutoring with her. The boys need nothing more to take on the challenge! "The VP’s niece" is again sidelined from the plans. Between two trips to the restroom because of sharp period pains, Simone tells Michèle she should show them she’s not a goody-two-shoes by stealing them herself.

It’s a good thing Laubrac’s there, because Michèle is very upset with Jean-Pierre and Simone. She hangs out at the student lounge where she tells everyone what she witnessed at the cinema and the rumors take off. The regional Latin contest is coming up for Jean-Pierre: he knows he can’t screw it up…

Michèle’s parents are worried she hasn’t come home yet. The Principal gives Bellanger an ultimatum: if Michèle did start the rumors about Jeanne, he wants to talk to her today. When Paul learns that she has eloped with his protégé, he goes looking for them. But in fact, he admires their boldness… The students improvise a surprise-party at Pichon’s to celebrate the end of the school year!