A patriotic but short American man tries without luck to qualify for the Army, but can't get in until a knock on the head raises a lump high enough for him to pass the height requirement. Meanwhile, his lady friend decides to become a Secret Service agent, though she is unable to keep the fact a secret, even from the German spies she hopes to apprehend.

During World War I, Herr Dresser, a German-American professor from West Hoboken, New Jersey, invents a "mustache fixer," which stiffens the whiskers, making the wearer look very fierce. Much to the consternation of Dresser's daughter Elsie, a patriotic American, Kaiser Wilhelm calls them to Berlin to begin mass production of the tonic for the German army. Elsie's boyfriend, Teddy Swift, is particularly disturbed by this turn of events and decides to earn enough money to follow her to Germany. When the United States joins the war, Teddy is among the first to enlist, and soon he finds himself in Berlin trying to help Elsie escape from prison. After several narrow escapes, the two make their way to the mustache factory and blow it up. Brought before the Kaiser, they are rescued when American troops storm the palace, and the Kaiser loses his mustache and the war.