Plato's Stepchildren is excellent. I got that the humiliation scenes were meant to horrify, when I was 10 seeing it on first run. I get this chill when Parmen asks McCoy "How can you let this go on?" Michael Dunn is incredible.
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AtCSL--- I'm glad fan opinion seems to shifting toward this as worst episode. I have always maintained, though, that they all have good stuff in them, because a very dedicated, talented team of professionals who believed in ST tried as hard as they could, to make bad stories as good as they could get, compensating as best they could for FF's decisions. Everyone was always in character!
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I can think of only one scene, ever, where Star Trek ceases even to BE Star Trek. That's the climactic scene in this story. All sense and all science fiction disappear. I am very aware when magic and the supernatural creep into what are supposed to be science fiction stories. All of a sudden, Kirk talks like he's in a children's fairy tale, and he is. He teaches the kids that ugly equals evil, by predicting Melvin is about to show us his ugly evil, which he then does. So it's not just a kiddie show but one teaching a bad lesson.
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Spock makes speeches about "evil", a basically magical concept. The backstory he discovers about the people the Gorgan belongs to seems supernatural. Still, until that last scene, they could still have pulled this one out of the fire... it could have been wrapped up in some SF fashion...
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It starts out as if it could be a good and smart episode. McCoy has some good, adult lines. The guards' beam out into space is jarring. This toughens the story up nicely. Scotty getting all fussy about his engines was fun. The image of the knives in space left a big impression with me.