▁sp y ▁in ▁Naz i ▁Germany ▁during ▁World ▁War ▁II . ▁He ▁is ▁a ided ▁by ▁a ▁French ▁agent , ▁Sus anne ▁Duch ard , ▁played ▁by ▁Christ ine ▁Car ère . ▁ ▁Plot ▁In ▁Naz i ▁Germany ▁during ▁World ▁War ▁II , ▁David ▁March ▁( Ro bert ▁G ou let ) ▁is ▁an ▁American ▁tra itor ▁who ▁has ▁been ▁given ▁wide ▁access ▁to ▁travel ▁as ▁he ▁wishes ▁within ▁Germany . ▁Un be known st ▁to ▁the ▁Germ ans , ▁March ▁is ▁actually ▁an ▁American ▁sp y , ▁the ▁last ▁remaining ▁from ▁a ▁sp y ▁ring , ▁known ▁as ▁Blue ▁Light . ▁As ▁time ▁goes ▁on , ▁he ▁has ▁been ▁able ▁to ▁work ▁his ▁way ▁higher ▁and ▁higher ▁within ▁the ▁Naz i ▁intelligence ▁appar atus , ▁however ▁he ▁is ▁sus pected ▁by ▁a ▁Naz i ▁Gest ap o ▁officer , ▁Captain ▁El m ▁( W erner ▁Peters ). ▁Al ong ▁the ▁way , ▁he ▁meets ▁Sus anne ▁Duch ard ▁( Christ ine ▁Car ère ), ▁a ▁French ▁agent , ▁who ▁he ▁has ▁a ▁rom antic ▁inter l ude ▁with , ▁and ▁persu ades ▁her ▁to ▁help ▁him . ▁ ▁El m ▁fost ers ▁a ▁plan ▁to ▁expose ▁March ▁by ▁taking ▁him ▁to ▁Spain ▁to ▁meet ▁with ▁a ▁British ▁scient ist , ▁Guy ▁Sp a uling ▁( Donald ▁Har ron ), ▁who ▁wants ▁to ▁defect ▁to ▁Germany . ▁El m ▁knows ▁that ▁Sp a uling ▁is ▁a ▁British ▁agent . ▁Sp a uling ▁asks ▁March ▁to ▁kill ▁him , ▁in ▁order ▁to ▁validate ▁March