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.