After graduation, it's easy to lose touch with one another. This is the case for Piero, a DJ who made up his marriage to keep his lovers under control, Virgilio, his long-time frenemy, Lorenzo, who still lives with his parents, and Luisa, a single mother to little Emma. Then there's Francesca, the sex-addicted chef, and Serena, who knows only a life of luxury and worries about her daughter Lucrezia's affection for a working-class descendant of Gigi, the bus driver. These former classmates haven't seen each other in 20 years. Then, a bizarre twist of fate strikes: the Ministry of Education nullifies their exam because one of the examiners wasn't even a graduate. So, as they approach their 40s, the only option is to retake not just the graduation exam but the entire school year. Thus, they all find themselves back in the classrooms of Liceo Mamiani.

After copying a test in class, Piero and Virgilio reconcile. The DJ had mistakenly thought his friend had spent a romantic night with Anita, his ex-girlfriend. However, that was not the case. There is a common issue they all face: how to make their philosophy teacher, Claudia, more lenient. She plays a prank on Piero, who has decided to charm her during a private lesson. The classmates decide to skip school and enjoy a day at the beach. Only Serena, running low on funds, is forced to find a job with a delivery company. Their return home after a day of beach games will hold surprises for each of them.

Claudia decides to perform as a dancer in a shady club to raise money for Simona's medications. Piero, dealing with more trivial matters, alters childhood photos of Virgilio's daughter to pass himself off as a father to Cinzia. The day of the parent-teacher meeting arrives, and among the experienced parents, some attempt to bribe the teachers, while Lorenzo attends with his father. Francesca opts to have her tutor represent her to dodge Daniele's gaze, but he eventually persuades her to go out with him. Piero also pressures Claudia into inviting him to dinner, while Luisa agrees to meet a suitor she met during a speed dating event. Lorenzo was there with her, but he realizes he is actually more interested in her friend.

The school occupation brings various tensions to light. Daniele is making futile attempts to get closer to Francesca. Piero successfully lures Claudia into the staff room, pretending to save her from the frenzied students outside. This serves as a cover for their first kiss, but the teacher immediately withdraws, claiming "professional ethics." Virgilio is aware of Doriana's boyfriend, yet she seems captivated by an enigmatic admirer who sends her sweet messages. Who is this person?

Just a few days ahead of their school trip to Sicily, the romantic endeavors of our main characters seem to be hitting a rough patch. Gigi and Serena are in a heated argument because Gigi has discovered that Serena has been hiding her true situation from him, revealing that her husband has left her and their daughter without any support. Doriana finds out that her mysterious admirer is none other than Virgilio; feeling disappointed and intimidated by their significant age gap, she abruptly pushes him away. Meanwhile, Lorenzo and Luisa are increasingly distracted by Paola and Flavio, their new love interests. Lastly, Piero continues to charm his current lovers, though he now appears to lack his usual confidence.

Just back home, Lorenzo is struck by a debilitating psychosomatic fever. He regrets not having found the right words to say to Luisa after their enchanting night in Sicily. Serena distances herself from Gigi and makes a serious attempt to reconnect with Giuseppe, trying to restore the affluent lifestyle she enjoyed before her husband's disappearance. The fallout from Serena's split with Gigi causes a definitive strain on the relationship between Savino and Lucrezia. Meanwhile, Doriana is sending out tentative signals to Virgilio through text messages, but he seems hesitant, still caught up in thoughts of his wife, Bruna.