A Russian prince disguised as a worker and a cafe singer secretly involved in revolutionary activities fall in love.

It is the fate of a small frontier town, adjoining the no-man's-land where the Russians and Austrians are fighting out one of the final campaigns of World War I, to be occupied one day by the Russians, the next by the Austrians, and the inhabitants soon acquire a complacent view of the changing allegiances. To the town comes Ann Warschaska, intent on avenging the suicide of her sister, who has killed herself after being betrayed by an Austrian officer. She knows no more about his identity than the number of his room at the "Hotel Imperial".