In the years before World War I, a love affair takes place between an American pilot named Jack Ames (Jack Whiting) and a French spy named Madeleine Aubert (Irene Delroy). Madeleine leaves her American fiancé to join her father (John St. Polis), another French spy, at an estate in Germany. Her father instructs her to accept the invitation of a Prussian officer, Eric von Coburg (Bramwell Fletcher), to live at his estate for a month. Jack, believing that Madeleine no longer loves him, joins the Lafayette Escadrille, a squadron of French and American flyers. His first duty is to take a French spy, dressed as a Prussian officer, over the lines. The spy is wounded during the crossing, however, and Jack must take his place. The French spy tells Jack that another French spy will signal him on the piano, playing a happy tune if danger threatens and sad music if the house is safe. Jack puts on the spy's uniform and arrives to find Madeleine at the piano. After Madeleine explains her mission, they continue to exchange messages. The Germans, however, become suspicious of Madeleine and on a night Jack is set to visit, she is entertaining officers of the German intelligence. One of them asks her to play sad music. Realizing that this will place Jack in danger, she signals Jack in Morse code with her left hand. The officers discover the trick, and Jack and Madeleine are captured, accompanying her father to the firing squad.