The film is based on the autobiography of , mayor of Kolberg in Pomerania, and on a play drawn from the book by Paul Heyse. It tells the story of the defence of the besieged fortress town of Kolberg against French troops between April and July 1807, during the Napoleonic Wars. In reality, the city's defence, led by then-Lieutenant Colonel August von Gneisenau, held out until the war was ended by the Treaty of Tilsit. In the film, the French abandon the siege.