Theodore Honey (James Stewart) is a mathematician charged with discovering what caused the crash of a "Reindeer" airliner. As he travels to investigate, he realizes en route that he's flying on the very same type of airplane. Convinced it will suffer a similar accident, he deliberately sabotages it once it lands, and soon finds himself defending his sanity in an English courtroom. Fortunately, a sympathetic actress (Marlene Dietrich) and a stewardess (Glynis Johns) come to his defense.