Mary is a nursing sister at a Lancashire prison camp for the housing and treatment of German POWs. Life at work is difficult but fulfilling; life at home a constant round of arguments - often prompted by her fly-by-night sister, Ellen, the apple of her shorttempered father's eye. Then Frank turns up at the house one night - a guard at the camp, he's been watching Mary for weeks - and won't leave until she agrees to walk out with him. Frank Shuttleworth is a difficult man to love and it's not long before Mary gives him his marching orders. But Shuttleworth won't take no for an answer and the gossips are eager for their next victim, for the least hint at fraternization with the enemy. Now, not only Mary's happiness but her very life is threatened by the most dangerous of wartime secrets...