In the Diplomatic Service (1916)

Foreign powers keep getting their hands on U.S. military secrets, so the head of the American diplomatic corps calls in his nephew Dick Stansbury to help. Stansbury knows that Doctor Montell is at the bottom of this, so he poses as an inventor of an innovative aerial gun. This sparks the doctor's interest, and when they both attend a weekend party at the Ryerson estate, Montell tries to get Stansbury to sell the gun to his country.