In 1944, American naval officer Lt. Wyatt Paxton arrives in London to prepare for the Allied invasion of France. He works closely with Dorothy Fairfax, a "Wren" in the Women's Royal Naval Service. Dorothy pieces together reconnaissance photographs with thousands of holiday snapshots of France--including those of her own family's summer home--in order to create accurate maps of Normandy. Maps that Wyatt will turn into naval bombardment plans. As the two spend concentrated time together in the pressure cooker of war, their deepening friendship threatens to turn to love. Dorothy must resist its pull. Her bereaved father depends on her, and her heart already belongs to another man. Wyatt too has much to lose. The closer he gets to Dorothy, the more he fears his efforts to win the war will destroy everything she has ever loved.