Jiří Kroupa (Jiří Sovák) is a man in his forties who is a team leader in a factory manufacturing agricultural machinery. He has an opportunity for promotion, but for that he needs to obtain a highschool graduation diploma. Kroupa resists vehemently, but is finally persuaded to enroll in the evening classes at a highschool where he is joined by a motley group of men and women of the same age group. Having found themselves in school again, the middle-aged Kroupa and his fellow students soon start acting like teenagers and with this and the teachers who find themselves instructing people their senior in the evenings and their children during the day, situation quickly gets out of hand.