The Lady Vanishes (1979)

On a train travelling through pre-World War II Germany, American heiress Amanda Metcalfe Madvani von Hoffstetter Kelly (Cybill Shepherd) befriends Miss Froy (Dame Angela Lansbury), an older nanny. But when Miss Froy disappears, everyone Amanda asks denies ever having seen her. Eventually, Amanda persuades American photographer Robert Condon (Elliott Gould) to help her search the train, during which they discover that Miss Froy wasn't quite what she seemed.