Knatten and Janne, just released from the prison of Långholmen, meet a romantic Stockholm in the 40s. Knatten tries to earn money while Janne is looking for the music.

The rich, aristocratic Katarina Hassel have an architect renovate her mansion. Katarina fall in love with the young architect, Gunnar Stenwall. Alas, he doesn't fall in love with her. But perhaps if Gunnar would meet her identical sister, who works in Stockholm as a waitress, he would fall in love with her instead? So Katarina travels to Stockholm to act as her non-existing sister.