'The Lady Vanishes'

The IMDB one-liner for Alfred Hitchcock's The Lady Vanishes is "While traveling in continental Europe, a rich young playgirl realizes that an elderly lady seems to have disappeared from the train." Echoes of Agatha Christie's disappearance? Vanishing women is a fascinating metaphor in itself, but Christie must have made her way to Harrogate by train in order to disappear and there's a fair amount of gaslighting going on on both trains.

The film's script was by Sidney Gilliat and Frank Launder, adapted from the Ethel Lina White story “The Wheel Spins” (1936).