Sky Murder (1940)

Pat Evans is a German expatriate who is loyal to her new adopted home, the United States. A shadowy German bund operating in the Long Island area tries to recruit as the sophisticated but lecherous Andrew Hendon tries to physically coerce her into joining. While she is flying in the private plane of Cortland Grand, a rich friend of Nick Carter's, she knocks Hendon unconscious in self defense, but leaves him alive in a rear compartment of the plane. When the steward discovers the body, he finds Herndon stabbed in the throat by a nail file. Before the trip is over, the co-pilot is also stabbed to death. Luckily for Pat, one of the passengers on Grand's plane is famed New York detective Nick Carter. Although he is off-duty, the resourceful sleuth along with Beeswax, his bizarre sidekick, and beautiful Southern Chris Cross, a female gumshoe, breaks up a secret cell of Nazi saboteurs and FIfth Columnists.