On a train headed for England a group of travelers is delayed by an avalanche. Holed up in a hotel in a fictional European country, young Iris befriends elderly Miss Froy. When the train resumes, Iris suffers a bout of unconsciousness and wakes to find the old woman has disappeared. The other passengers ominously deny Miss Froy ever existed, so Iris begins to investigate with another traveler and, as the pair sleuth, romantic sparks fly.
This is a great adventure caper - Margaret Lockwood befriends a charming old lady - Dame May Whitty - in an hotel who subsequently disappears as they travel on a train back to England. She teams up with the pretty exasperating Michael Redgrave and together they try to find the old girl. Paul Lukas is the wonderfully understated doctor and Catherine Lacey has fun being the nun. There are also a few minor storylines running parallel with the search which add some humour and a little diversion as we discover that there are sinister forces at work. It's a simple but compelling Sidney Gilliat screenplay with Hitchcock at his suspenseful best.