The Deadly Game.

A pre-World War II saber-rattler that finds a munitions inventor kidnapped, a federal agent killed and a beautiful refugee mysteriously missing as Washington's deadly game of espionage and intrigue thunders on...as the FBI hunts the nation's invisble foes! They may have been invisible but their accents and billing names von Morhart, William Vaughn (William von Brincken already hiding under another name before hostilities were formally declared), Frederick Gierman and Walter Bonn---provide clues aplenty as to their country of origin and paymaster.