Swenko's wife, Hilda Riker (Lya Lys) finds out her husband is dead and recognizes Bancroft as an imposter. Before she can alert Garvey that there is a federal agent about, Gabby, posing as a taxi driver, follows Brass to Hilda's apartment and comes to his rescue.
An unwitting Garvey assigns Bancroft to board the U.S. Navydirigible USS Mason, which carries the newly invented "Inertia Projector", a sort of death-ray that can shut off an engine. Once aboard, Bancroft is to contact Garvey's henchman Rumford (Victor Zimmerman). Rumford is posing as an assistant to Dr. Finchley (Robert Warwick), a scientist working for the League of Nations, who invented the projector.
While he steals the plans for the inertia projector, Rumford orders Bancroft to destroy the dirigible, but Garvey and Rumford learn Bancroft is a government agent. When the dirigible crashes during a storm, Rumford takes the plans and leaves the unconscious Bancroft to die in the crash.
Brass is rescued and taken to a Navy hospital. Garvey tries to fly to Mexico with Rumford and the stolen documents. Brass alerts Saxby to Garvey's plan. In a spectacular air chase, the agents
catch Garvey's aircraft. They bring it down with the inertia projector, sending both spies to their death in a burst of flames.
Film reviewer Bosley Crowther, in his review for The New York Times, enjoyed 'Murder in the Air', "Ronald Reagan and the Warners' FBI agents have the situation well in hand. After some sixty minutes of highly incredible melodramatic incident, the government's prized 'inertia projector' is rescued from foreign hands and the saboteurs are either killed off or jailed. (The 'inertia projector' is an instrument which fouls electric current at the source; its amazing practicality is illustrated when it is focused on the plane in which the enemy agents attempt to flee the country.) Mr. Reagan, who had seen service previously with the Warners' FBI force, handles his role of counter-espionage agent with the customary daring. Eddie Foy Jr. has a few good comical moments, and Lya Lys of the golden tresses makes an attractive Mata Hari. The screen play by Raymond Schrock is compact, if not 'original', and the direction by Lewis Seiler is swiftly paced. All of which tends to make 'Murder in the Air' acceptable program fare."[4]
Aviation film historian James H, Farmer in Celluloid Wings: The Impact of Movies on Aviation (1984), described Murder in the Air as, "... an action-packed thriller."[5]
Legacy
Footage from the film is used in the 2020 documentary The Reagans to illustrate President Reagan's support for the Star Wars defense program, which conceptualized the capabilities of a similar device from the film.