Fritz Weineck (Horst Jonischkan), a worker’s son from Halle, loves music and hopes to make a living out of it one day. When his friend Alfons, a World War I veteran, gives him a trumpet as a gift, Fritz seems to be one step closer to his dream.

When Fritz realizes that workers still must desperately fight for their rights even after the end of the German Empire, he decides to use his instrument for political means. At a meeting of militant workers, he uses his trumpet as a signal horn. Fritz suffers a severe setback when he causes the death of a comrade during the fight arms depot. However, on March 13, 1925, he becomes a hero and communist martyr when his horn saves comrade Thälmann from the police.

Otto Gotsche's novel Our Little Trumpeter, which was based on real events, served as the literary basis for this biopic.