Jessica and Diana Mitford grew up in the same English aristocratic household and ended up on opposite sides of the twentieth century's defining political fight. Diana left her husband for Oswald Mosley, leader of the British Union of Fascists, and socialized with Hitler at close range. Jessica ran away to fight for the Republicans in the Spanish Civil War and later joined the American Communist Party. The film traces how the sisters' rivalry, present since childhood, hardened into ideology as Europe polarized in the 1930s, using archival photographs, newsreel footage, and historian interviews to place their story against the rise of fascism and the international left. It follows the family fractures that followed, including the sisters' lifelong estrangement, and sets their choices alongside those of their other siblings, who scattered across the same political spectrum. The result is a portrait of how family loyalty and political conviction pulled against each other inside one household during the interwar years.