 On a Paris bound airplane in 1945, Colonel Ralph Denistoun (Ray Milland), of British Intelligence, is being interviewed by American correspondent Quentin Reynolds,(playing himself). His story begins in Germany in 1939, before war had been officially declared, but he and fellow agent Richard Byrd (Bruce Lester), stationed in Germany, are being held prisoner, incommunicado, because of their knowledge of a deadly poison gas formula perfected by Professor Krosigk (Reinhold Schunzel) for the Nazi war machine. Escaping, Denistoun and Byrd go separate ways, agreeing to meet later at a Freiburgn sign post on the road near Eschbach. Denistoun is making his way through the woods when he meets Lydia (Marlene Dietrich), a Hungarian gypsy girl, who offers to help him. She pierces his ears for dazzling golden earrings, stains his skin, dresses him in Zigeneur clothes and teaches him to read palms. His disguise if perfect and he emerges unharmed from several encounters with Nazi patrols. Byrd is killed by the Gestapo, leaving Denistoun on his own to contact Krosigk, a violent anti-Nazi, who gives the Britisher the secret of the poison gas. Aided by Lydia and Zoltan (Murvyn Vye), the gypsy leader, Denistoun escapes from Germany across the Rhine to France, with a promise to return to Lydia after the war.