Nick Carter, Master Detective (1939)

Famed New York detective Nick Carter arrives incognito at a California airplane factory at the behest of owner Hiram Streeter. Despite seemingly thorough precautions, a gang of saboteurs and shadowy foreign agents are able to smuggle out the secret blueprints for innovative new planes and sabotage prototypes during testing. With the aid of eccentric detective Bartholomew and spunky nurse and female pilot Lou Farnsby, Carter is able to expose the fifth columnists as well as the traitors that are helping them.