In 1944, while dealing with a Lisbon double agent, Maj. Jefferson Pike of U. S. Intelligence is abducted by Germans, drugged, and flown to Bavaria. He has been fully briefed on D-Day invasion operations in Normandy, and the Germans mean to pry this information from him through an elaborate trick. Pike awakens in what appears to be an American military hospital in occupied Germany: the staff speak English, newspapers are dated 1950, and the war is apparently over. Maj. Walter Gerber, seemingly an American psychiatrist but actually a Nazi, tells Pike he is an amnesia victim but can be cured by recalling the events before, during, and after D-Day. (Gerber has only 36 hours to secure this information; thereafter, it will be forced out of Pike through torture.) Pike discusses Normandy, but through a giveaway detail, he discovers the Nazi scheme. He confronts Gerber and Otto Schack, a Gestapo agent, and tries to persuade them that he has been giving false information. He is dispatched for further questioning, however, accompanied by Anna Hedler, a German nurse pretending to be his wife. Schack doubts that Normandy is the landing site, and the three men play a cat-and-mouse game utilizing this skepticism. The failure of the initial deception having put Gerber out of favor with the Gestapo, he entrusts valuable papers on his amnesia experiments to Pike, helps him and Anna escape to the Swiss frontier, and then commits suicide. The Normandy landings begin and the enraged Schack pursues Pike and Anna to the border; but he is shot down by an anti-Nazi guard who has arranged for the escapees' safe crossing. Once in Switzerland, Pike prepares to depart for London, knowing that he and Anna will meet at the end of the war.