In war-torn London during World War II, Catrin Cole, a former secretary, lands a job with the British Ministry of Information. Her task is to write scripts for propaganda films designed to lift morale amongst the British public and encourage American intervention. Working under the skeptical and chauvinistic Tom Buckley, Catrin battles gender bias to carve out a space for herself in the male-dominated industry. As she begins to contribute valuable and resonant scenes to their latest film about the evacuation of Dunkirk, her fresh perspective shines through, offering a sense of authenticity and hope amid the chaos of war.

Catrin's talent catches the attention of the film's aging but charismatic lead actor, Ambrose Hilliard, who struggles with the reality of his fading fame. Meanwhile, Catrin's personal life is complicated by her relationship with her artist husband, whose career is faltering amidst the turmoil of the times. As the production moves forward, Catrin and her colleagues face tremendous logistical and emotional challenges, navigating the dangers of wartime and their own evolving personal dynamics. The process of making the film proves transformative for Catrin as she discovers her own strength and voice amidst the collective efforts to bolster a nation's spirit during its darkest hours.