Inspired to help her country at the outbreak of World War I, Elsa Elsbergen applies as a nurse's aide at the Viennese Red Cross station but is turned down because of her reputation as a "woman of experience." However, Elsa's pleas to join in the war effort are overheard by an Austrian military officer, who refers her to his superior, Major Schmidt. Convinced that Elsa will make an effective spy, Schmidt asks her to romance Captain Otto von Lichstein, a suspected traitor. On the same night that she is introduced to Lichstein, Elsa is hit accidentally by the carriage of Count Karl Runyi, a young Hungarian naval officer. Taken with Elsa, Karl begins to call on her, unaware of her past or her work as a spy. Equally enamored of Karl, Elsa neglects her duties with Lichstein, and her budding romance is reported to Schmidt. At a beer garden, Captain Kurt von Hausen deliberately insults Elsa and provokes Karl to challenge him to a duel. In spite of Hausen's superior skills as a marksman, Karl beats his opponent and then proposes to Elsa. Overwhelmed by Karl's unquestioning devotion to her, Elsa accepts his proposal and then tells Schmidt that, to protect her engagement, she is abandoning her mission with Lichstein. Later that day, however, Karl confesses to Elsa that he turned down an opportunity to join an elite submarine group in order to remain with her. Eventually Elsa convinces Karl to do his patriotic duty and vows to wait for him. Soon after his departure, however, Elsa resumes her work with Lichstein and writes to Karl that she has fallen in love with another man. At a party at Lichstein's home, Lichstein orders Elsa to entertain a junior Austrian officer and then pries information out of the drunken youth on the whereabouts of Karl's submarine unit. After Elsa alerts Schmidt about Lichstein's activities, she threatens Lichstein with a gun to prevent him from delivering his message. Lichstein struggles for the gun, and Elsa is shot in the chest. When Karl returns to Vienna a war hero, Elsa happily renews their engagement but says nothing about her encounter with Lichstein. Aware of Elsa's reputation, Karl's mother, Countess Runyi, threatens to expose her past to Karl until Katie, Elsa's housekeeper, informs the countess of Elsa's sacrifice for the war cause. Although moved by Elsa's heroism, the countess insists that her marriage to Karl would fail after six months. Elsa shows the countess a medical report that states that, as a result of her gunshot wound, she only has six months to live. Determined to have six months of happiness, Elsa marries Karl.