A musical comedy about two indistinguishably similar siblings who love music, but each of them is completely different. Pavel Fořt is a professor of classical music at a pedagogical institute, his brother is a jazz musician and plays music in America. When the twin brother suddenly appears in Prague, they switch roles.

The family is connected with Prague's "Kolbenka", the ČKD locomotive factory. Grandfather Antonín, already retired, son Rudolf, a master in the locomotive assembly section and grandson Antonín, a promising football player. The film also tells the story of Rudolf's daughter Vera - each generation has its own ideas about life and cannot identify with the others. The film is linked by retrospective sequences from the lives of Antonín the Elder and Rudolf, especially from the war years. It is a realistic take on working-class life, unencumbered by ideology (despite the opening dedication), featuring well-known and time-tested actors in mainly male roles.

A group of jolly young people work in the Prague Tesla factory, also spending most of their leisure time together. One of them, guitar player Zdenek, begins to shun his friends' company. He has fallen in love with Vera, who does not belong to the group. The happy-go-lucky young man already has several acquaintances and has his own method to get a girl: to take his motorcycle, his guitar and a bottle of wine and take her to a rented houseboat. Vera, however, is different and gets angry at Zdenek. But she is fond of him and thus eventually spends a whole evening with him on the houseboat. At a preventative medical examination, the doctor tells Vera she is pregnant.

An insight into the lives of adolescents, it is about an ordinary boy who falls in love with a student. But soon he faces a serious rival in the form of a local seducer...