Chief of the German secret service in Paris, Prince Kondemarck has been ordered to secure for his government the service of the most clever and beautiful woman obtainable. Liane Dore, widow of the late Sebastian Dore, who was killed mysteriously, agrees to serve on the prince's promise to reveal in one year the name of the man who killed her husband, against whom she has sworn vengeance. Unknown to Liane, the prince himself accidentally killed Dore who, posing as a bachelor, betrayed the prince's sister. In the course of their association as spies, Liane and the prince fall in love. When war comes, Liane throws her home open to wounded Frenchmen, and Baron Arnorld von Pollnitz, a German spy seeking revenge on the prince, denounces Liane as a spy. Arrested and sentenced to death, she is saved by the prince. After learning that her rescuer was her husband's killer, Liane is on the verge of betraying him when he produces letters which prove her husband's duplicity, and together they flee on board the prince's yacht.