The master of suspense, Alfred Hitchcock, weaves a knotty yarn of intrigue in this early outing. Young, beautiful, and spoiled Iris Henderson (Margaret Lockwood) is wrapping up a ski vacation before unenthusiastically returning to London to be married. In the hotel, she meets an elderly governess en route to home, Miss Froy (Dame May Witty), as well as an unbearably rude music scholar named Gilbert (Michael Redgrave). Then, just before boarding the train, Iris receives a blow to the head and is taken under the protective wing of Miss Froy. Their conversation is polite and uneventful. Iris finally dozes off and when she comes to, Miss Froy is nowhere to be found, and no one on the train recalls seeing the governess. Thwarted at every turn in her search, Iris finds only one ally, the unbearable but handsome Gilbert. As their search begins to seem futile, Iris starts to suspect she is losing her mind. Then several people on the train--including a shifty physician and a mysterious nun--reveal nefarious motives beneath their innocent facades.