This is both a solid version of the story idea here titled "Into Thin Air", and a nice opportunity for Pat Hitchcock to take a starring role that, for the most part, also plays to her strengths. The story is an interesting one, and has been used from time to time in various forms, with Alfred Hitchcock himself having used a variant of the basic idea in "The Lady Vanishes". Here, it fits the half-hour anthology format pretty well, using the running time to draw out the mystery just long enough, without building up undue expectations for the resolution.
Pat Hitchcock plays a young woman traveling in Paris with her mother, and experiencing a series of disorienting and frightening events when her mother becomes ill and then disappears. Everyone around her insists on denying facts that she knows to be true, and indeed they always have convincing ways of proving her wrong. If you look at the story from a coldly clinical perspective, there are perhaps a couple of holes in it, and the resolution is perhaps not completely satisfying, but while it lasts, it succeeds quite well in establishing a convincing atmosphere of baffled fear.
In his closing appearance, Alfred Hitchcock plays the proud father, at least to the degree that his dry nature allows him to. Pat Hitchcock was never going to be a star, but she obviously shared her parents' enthusiasm for making good movies, and she always gave solid, believable, sympathetic performances in the various character roles in which she appeared. For Hitchcock fans, it's very nice to see her get this chance to take the spotlight herself for a little while.