When the Great War begins, English sportsman Cyril Hammersley is thought to be a slacker because he refuses to join the army for pacifistic reasons. His American fiancée, Doris Mathers, knows that he is not a coward, but she questions his patriotism when Sir John Rizzio intimates that Hammersly may be a German spy. During a dinner, Doris sees Captain Walter Byfield of the British War Office pass a cigarette paper packet to Hammersly. After Doris learns that Byfield was shot for spying, Hammersly confesses that he is an agent of the British Secret Service, and gives Doris the packet to hide. When Hammersly is captured and locked in Rizzio's country home, Rizzio visits Doris and sees the packet slip down her stocking to her ankle. After she retrieves it and he grabs it from her, Doris summons Scotland Yard. Rizzio's house is raided, the German spies are captured, Doris releases Hammersly, and the packet, containing an encoded message with plans to blow up London, is recovered.