Based on Nevil Shute’s novel, an eccentric engineer tries to persuade the aircraft industry that metal fatigue will cause old planes to crash.
Dennis Scott (Jack Hawkins) arrives to take over managing an aircraft company. Theodore Honey (James Stewart) is vibrating a plane to see if the tail will fall off. Scott gives Honey a ride home and talks with his daughter Elspeth Honey (Janette Scott) while Honey goes out to buy sherry. Honey says the tail will off after 1440 hours.
Scott talks with a test pilot who says they always blame pilot error. Scott warns the director Sir John (Ronald Squire). They send Honey on a flight to Labrador to investigate a crash there. The stewardess Marjorie Corder (Glynis Johns) helps Honey get comfortable, and he recognizes the film star Monica Teasdale (Marlene Dietrich). Honey gets to see the controls, and he learns the plane has flown 1422 hours. He warns the captain that a plane crashed in Labrador after 1407 hours and tells him to turn back and land. Honey thanks Monica for making people, like his late wife, happy. The captain makes an emergency landing. Monica tells Honey that he must have made a miscalculation. The captain orders an inspection and forbids Honey from flying.
Marjorie feeds Honey in a room, and he urges her to live and have a family. Honey goes on the plane and causes it to collapse. Sir John gets a call from the head of the airline. Monica took another plane and tells John and Scott that Honey should be supported. Honey confers with John and Scott. John tells Honey that they want to test his sanity.
Honey finds Marjorie at home in a robe, and she serves him food. Honey admits he made a mistake in damaging the plane. Marjorie dresses as a nurse and lets Monica in. Marjorie is a widow, and Monica says she is going to California. Elspeth comes in, and Monica gives her a present.
Honey tests the plane in his lab up to 1522 hours. He tells Marjorie that the tail did not fall off. She encourages him. Elspeth cries and tells her father to go away. At a board meeting Honey says he stands by his work and resigns so he can try to stop the planes even if he is arrested. At home he tells Marjorie about it and shows her the money he has saved. John and Scott learn that the tails are falling off the old planes. The tail falls off Honey’s test plane, and he realizes that he did not factor in the temperature correctly.
This story dramatizes the advance of scientific knowledge and how it can affect people’s lives if the lessons are not applied. Scientists experiment in order to predict the future so that disasters may be avoided; but any new theory is usually met with skepticism before it is proved to be correct.