In Hamburg in 1939, Peter Müller and Thomas Berger join their friends Arvid and Otto at a swing club called the Bismarck, where the night hums with jazz and carefree dancing that feels temporary under the tightening grip of the regime.
Peter goes home to find his mother in an argument with the Nazi Blockleiter. Herr Knopp, head of the local Gestapo, arrives and dismisses the Blockleiter. He begins questioning Frau Müller about connections to some of her late husband’s friends. Peter’s father had been accused of communism, and the confrontation leaves a lasting scar on the family.
Arvid’s house is disturbed when Thomas accidentally ruins one of Arvid’s prized records. Upset, Arvid kicks them out. To make amends, Peter and Thomas steal a radio from a bakery, a radio Peter knows was taken from a ransacked Jewish home. Thomas escapes, but Peter is caught. Herr Knopp, who is attracted to Peter’s mother, intercedes for him; in return, Peter must enroll in the Hitlerjugend. Thomas also joins, telling Peter they will enjoy both the privileges of Hitlerjugend membership and the pleasures of being Swing Kids.
Arvid is confronted on the street by a group of Hitler Youth, including former friend Emil. They beat him and break his hand, threatening his work as a jazz musician.
Peter, who has a job delivering books, is asked to spy on his boss, whom the Nazis suspect is working against the Reich. In HJ school, the boys are encouraged to spy on their friends and families. Thomas accuses his father of insulting Hitler, hoping to cause trouble for him, but is unnerved when the Nazis come to his home and take his father away. His subsequent attempts to resume his friendship with Peter and persuade him to collaborate with the Nazis are tinged with fear.
Arvid overcomes his injury and is able to play music again. However, while working at a jazz club, he refuses to play a German song, lashing out at the club’s patrons for being blind to the Nazi agenda. Peter is sympathetic but Thomas loudly argues the Nazi side. Peter angrily proclaims Thomas to be a "fucking Nazi" and storms off. Blacklisted from playing in clubs, Arvid realizes there is nothing for him in Germany and dies by suicide.
As Thomas begins to believe fully in Nazi ideology, Peter feels as though there is no hope for him. Peter, disenchanted with how his life is coming apart, dresses up and goes to a swing club which is scheduled to be raided by members of the Hitlerjugend. As Thomas begins assaulting the club’s patrons he attacks Peter; however, during the fight Peter is able to reach Thomas. Thomas begs Peter to run away but Peter won’t. As Peter is driven away by the police, his younger brother Willi loudly shouts Swing Heil! over and over again, proud that his brother stood up for being a swing kid.
Epilogue text reveals that a second generation of Swing Kids lived to see the Nazis defeated.
