After nurse Evelyn Vail, who was convicted of poisoning a patient, is paroled from prison, she returns to Los Angeles and reunites with her friend, Helen Gilbert. Helen tells Evelyn that Carl Peters, who was also implicated in the crime, is about to be executed in Sing Sing prison in New York. Evelyn is concerned because her former employer, Dr. Jim Moffat, remains in prison and she decides to break her parole in order to get a confession from Peters that would clear her and Moffat of the crime. On board an airliner, Helen makes the acquaintance of John Robinson Gordon, who is carrying a revolutionary munitions formula to Washington, D.C. When the plane makes a stopover in Dallas, Baker, a passenger who has apparently been poisoned, leaves the airplane. Back in the air, Gordon's bodyguard Lieutenant O'Brien is poisoned and dies. Meanwhile, Evelyn's parole officer has learned that she is on board the plane and it is called back to Dallas. Evelyn is suspected of O'Brien's murder but Gordon claims that she was with him throughout the flight and convinces police officer Daniel J. Barrie to obtain handwriting samples from all of the passengers. Gordon suspects that O'Brien was poisoned during the first stop in Dallas because of a note found in the dead man's diary. Meanwhile, Baker returns to the plane and Gordon identifies him as the murderer and states that he poisoned himself in order to divert attention from his true action. Baker admits committing the crime because O'Brien sent his father to prison. Gordon then postpones his trip so he may accompany Evelyn to New York, but they arrive after Peters's execution. Gordon and Evelyn learn that before Peters died, he confessed to a priest, thus clearing Evelyn and Dr. Moffat of the crime. Happily, Evelyn and Gordon embrace.