A widow spies for Austria and uses her wiles to survive in Russia; but later she lets the Russian spy escape and suffers the consequences.
In 1915 Vienna after a suicide widow Marie Kolverer (Marlene Dietrich) says she does not fear life nor death. She invites a man (Gustav von Seyffertitz) to her room. When he asks her to spy against Austria, she has a policeman arrest him. He is the head of the secret service and summons Marie to his office, hiring her to spy for Austria as X-27. He suspects Col. von Hindau (Warner Oland) is a traitor. At a masked costume party Marie meets Col. Kranau (Victor McLaglen) and Hindau, who takes her home. The secret service chief calls Hindau about invisible ink so that Marie can search. The butler says there are no cigarettes, but she finds one in Hindau's coat. Hindau takes a note from it, surrenders to her, and then shoots himself.
Marie finds Kranau gambling and refuses to give him the kiss she promised; so he leaves. The secret service chief sends Marie on a plane, but Kranau comes into her apartment and reads her instructions for Russia. He kisses her and says he is leaving Vienna. Marie has a gun, but he has removed the bullets. Kranau admits he is a Russian spy and leaves while he can. Marie flies in a storm. In Russia Kranau hears the attack plans. A Russian officer finds a woman, who is willing and is Marie disguised as a peasant. Kranau remembers her cat and asks about her. Marie writes music. Kranau breaks in and finds the Russian unconscious as she tries to escape. Kranau has her brought back and searches her. He tells her to play the music she wrote; suspecting it is a code, he burns it. Marie learns she will die at dawn and says she wants to be with him. They drink to love and excitement, and he is drugged. Marie returns and writes her composition for officers.
Marie sees captured Kranau, who refuses to give his name. Marie says he is a spy and asks to question him. Alone with him, she drops her gun, and Kranau goes out the window and flies off. Marie says she loved him and is sentenced to be shot. She asks a priest for a dress and a piano. Marie declines a blindfold, and the officer refuses to kill a woman. He is replaced, and she is executed.
This well-crafted drama shows a woman using her sexuality to serve her country by spying and to enable her to escape death; but the love that results leads her to save her lover even though it endangers her country and means her death. Her dignity has such an affect on one young officer that he refuses to kill anymore a strong anti-war moment.