While Still We Live by Helen Macinnes

English girl Sheila Matthews’ innocent holiday to Poland becomes a nightmare when the German Army invade in the summer of 1939. Working for the Polish underground as a double-agent, she plays a dangerous game, and is soon suspected by the Germans. Forced to flee to the forest and hunted by a ruthless German officer, she must rely on the dashing Captain Adam Wisniewski to help her home.