The action takes place in Paris during World War 1. Lili Smith, well-known British music hall performer, actually works for the German government. As a spy, her task is to gather information on the plans of the warring parties. Major Kurt von Ruger, camouflaged as her uncle, is her connection to the German military. Fulfilling her mission, Smith tails the exalted American pilot Major William Larrabee. By dedicating almost all her time to this task, she soon becomes fascinated by the major and falls in love with him. Therefore, she is no longer able to betray him.