Margaret Lockwood plays an American socialite in Europe in this Hitchcock mystery-thriller. The night before she is to leave, Lockwood meets a kindly middle-aged lady who is fascinated with European music. The next day the two ladies sit together on the train to talk. Being a bit disoriented, Lockwood takes a short nap however when she wakes up Ms. Froy is mysteriously gone. Seemingly no one remembers seeing the woman and no one will believe Lockwood. Finally, she teams up with a man who she had a run in with the night before (Michael Redgrave). Together they try to figure out what has happened to the lady. Finally discovering the truth, they come under great danger and must fight for their lives and those of the other passengers. Hitchcock does it again, bewildering the mind and making us intrigued at the same time.