During the closing days of the Second World War, six members of his Royal Canadian Air Force fighter squadron are killed due to a command decision made by pilot Ted Stryker (Dana Andrews). Years later, in civilian life in Ottawa, Ontario, Canada, a guilt-stricken Stryker goes through many jobs, and his marriage is in trouble.
Stryker finds a note at home: his wife Ellen (Linda Darnell) has taken their young son Joey and is leaving him, flying to Vancouver. He rushes to Ottawa Airport to board the same flight, Cross-Canada Air Lines Flight 714. He asks his wife for one last chance, but Ellen says that she can no longer love a man she does not respect.
The routine flight becomes deadly when stewardess Janet Turner (Peggy King) begins the meal service. Meat or fish are the options. When a number of passengers begin feeling sick, a doctor (Geoffrey Toone) aboard determines that there must have been something wrong with the fish.
While attending to others, including Stryker's son, the stewardess and doctor discover that both the pilot and co-pilot have also become seriously ill. Although it stays in the air on autopilot, no one is left to fly the airliner. After the stewardess checks with other passengers, she determines that Stryker is the only one with flying experience, but he has not flown in 10 years and has no familiarity with aircraft of this size. Due to dense fog on the ground obscuring the runway, Flight 714 must bypass Calgary and all other intermediate airports, to continue on to Vancouver.
Stryker's superior in the war, the tough-minded Captain Treleaven (Sterling Hayden), is summoned to Vancouver Airport to give him instructions about how to land the aircraft. Ellen joins her husband in the cockpit to handle the radio. Ordered to remain airborne, Stryker makes another command decision to land the airliner because passengers will die if they do not get to a hospital soon.
Zero Hour! was an adaptation of Hailey's original 1956 Canadian Broadcasting Corporation teleplay Flight into Danger. Hailey also co-wrote a novel with John Castle based on the same plot titled Flight Into Danger: Runway Zero-Eight (1958).
Principal photography took place from May 8–28, 1957 with retakes on July 23–24, 1957. The primary filming location was Santa Ana, California. Nightclub and television performer Peggy King made her feature film debut in Zero Hour!, recording the song "Zero Hour" for Columbia Records to coincide with the film's release.
The New York Times reviewer Bosley Crowther called Zero Hour! an "exciting contemplation of a frightening adventure in the skies" based on a "good terse script ... Dana Andrews as the hero and Sterling Hayden as the captain are first-rate in these roles, keeping them hard and unrelenting." Time magazine, however, called the script a "bloopy inflation of a 1956 television show" and said its "moral struggle comes off fairly well, but the general situation is as patently contrived as one of Walter Mitty's daydreams."
In 1971, the film was reprised as a made-for-television movie, Terror in the Sky, a Movie of the Week special with Doug McClure in the title role. Zero Hour! was also used as the basis for the parody film Airplane! (1980). Because Zero Hour! was owned at the time by Paramount Pictures, the makers of Airplane!, also a Paramount feature, were able to use the screenplay almost verbatim.