The newly wed Jimmy and Maggie McDougal learn the news of Maggie's pregnancy just weeks after Jimmy is called to duty in World War II. Frequent letters and their deep love for one another provide comfort while they are apart. But, suddenly, Jimmy's letters to Maggie cease and the Army confirms the worst of her fears. Alone, Maggie raises their daughter, Mary, who never knows her father. Some sixty years later, Maggie is diagnosed with a terminal illness and eventually moves in with Mary, who becomes her caretaker. At about the same time that Maggie learns of her diagnosis, the Army, during a base closure, discovers a World War II letter addressed to her. While Mary is coping with a dying mother, a demanding job and trying to learn as much as possible about the father she never knew, the Army is searching for the intended recipient of the World War II letter. Will Maggie succumb to her illness before the Lost Letter reaches her?