The promise is the story of three young women who, when the war breaks out, decide to join the Lotta-Svärd Association. Anna ends up in air traffic control, Mona in veterinary medicine and Ruth in the field hospital. Each of them receives training for their task, but cannot fully prepare for war. None of them can even guess what the given lLotta promise will demand from them. The promise describes young women’s longing for freedom, dreams and coming of age at a time when Finland was at war. It tells about women who pushed their own dreams aside and made a Lotta promise to the motherland. The work of these women, both on the home front and on the war front, was crucial in the small country’s struggle for independence. The film follows five years of Mona, Anna and Ruth’s life from 1939 to 1944.