Swat the Spy (1918)

Andrew Sheldon is so busy perfecting a new explosive for the United States effort in World War I that he fails to realize that his butler, cook, housekeeper and chauffeur are all German spies. His two mischievous daughters, Jane and Katherine, however, make life difficult for the spies by throwing pies at the Kaiser's picture and clipping the butler's long, Prussian-style mustache while he sleeps. When Andrew's wife announces that she is pregnant, he tells the girls that he has written a letter requesting a baby brother for them, whereupon they decide to steal the letter, convinced that two children are enough for their family. Breaking into Andrew's laboratory, they take the "letter," actually the secret formula, but after Andrew reveals that his plans are missing, the butler enters the laboratory and seizes the invention itself.