1946, Manhattan. Passing through Grand Central Terminal on her way to work, Grace Healey finds an abandoned suitcase tucked beneath a bench. It contains a dozen photographs-- each of a different woman. In a moment of impulse, Grace takes the photographs and quickly leaves the station. She learns that the suitcase belonged to a woman named Eleanor Trigg, leader of a network of female secret agents who were deployed out of London during the war. Twelve of these women were sent to Occupied Europe as couriers and radio operators to aid the resistance, but they never returned home, their fates a mystery. Setting out to learn the truth behind the women in the photographs, Grace finds herself drawn to a young mother turned agent named Marie, whose daring mission overseas reveals a remarkable story of friendship, valor, and betrayal.