Death Flies East (1935)

Evelyn Vail (Florence Rice) is a nurse convicted of poisoning a patient. Out on parole, Evelyn decides to fly to Sing-Sing and confront death row inmate who accused her of the deed in the first place. On board the airliner, Evelyn makes the acquaintance of John Robinson Gordon (Nagel), who is transporting a revolutionary munitions formula to Washington, D.C. Another passenger, Baker (Robert Allen), complains of having been poisoned and leaves the plane during a stopover in Dallas. Back in the air, Gordon's bodyguard, Lieutenant O'Brien (Fred Kelsey), suffers the same fate, but this time the poison proves fatal. The plane returns to Dallas, where Police Captain Barrie (William B. Davidson) accused poor Evelyn of the crime. Happily, Gordon can prove otherwise and the real culprit is unmasked.