Ann Todd was a fine actress. However, you wonder why anyone would consider casting her in this episode, as her father is played by John McIntire and he sounds very American and she clearly is English...very English. So, at times while I was supposed to be watching the plot, I found myself wondering WHY they cast the film the way they did! Despite the poor casting decision, the show is pretty good though certainly not among the best of the series' shows.
The show begins with the father planning on going on a trip without his adult daughter (Todd). However, he's apprehensive to go because she has a history of depression and suicidal ideation. So, to set his mind at ease, he visits his daughter's therapist to get his recommendation. And, in the process, you learn through flashbacks about the daughter and her marriage to a god-awful jerk of a man who has since divorced her. What's next? See the show.
The ending to this one is appropriately dark for the series and unlike many dark endings, Hitchcock himself doesn't provide some epilogue which says the person was caught for their evil deeds and punished...a MAJOR shortcoming for many shows.