Agent Saxby, the head of the Secret Service in the U.S. Treasury Department, assigns agent Lieutenant "Brass" Bancroft to impersonate a deceased spy Steve Swenko. Gabby Watters, Brass's assistant, finds a letter in the dead spy's shoe, addressed to Joe Garvey, the leader of a group being investigated by the Rice Committee on Unamerican Activities. Swenko's wife, Hilda Riker 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. Navy dirigibleU.S.S. Mason on which an "Inertia Projector," a death-ray/laser gun, is mounted. Once aboard, Bancroft is to contact Rumford, a spy posing as an assistant to Dr. Finchley, a member of the League of Nations. 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 steals the plans and leaves the unconscious Bancroft to die in the crash. After Brass is rescued and taken to a Navy hospital, Garvey plans to fly Rumford and the stolen documents across the border. Saxby is alerted, and in a spectacular air chase, Garvey's aircraft is shot down by 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. 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." Aviation film historian James H, Farmer in Celluloid Wings: The Impact of Movies on Aviation, described Murder in the Air as, "... an action-packed thriller."
