[TOS] Season 2, Episode 14 (Netflix: S2 E14): Wolf in the Fold
It’s an episode centered around Scotty, but it’s the beginning of a trend in Star Trek where a side character is usually cooler when they don’t have an episode focused on them. We mainly just get to see Scotty look confused for 30 minutes. The murder mystery doesn’t really work either. It starts to become comical how the writers keep one-upping themselves with situations that make Scotty look more and more guilty. It goes on for too long, and we of course never believe Scotty goes around killing women for no reason.
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Read more at Memory Alpha
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Notes:

The dancer was stabbed and Scotty was found next her body holding a knife. He says he doesn’t remember what happened.

To find out if Scotty murdered someone, they put him in a locked room alone with a woman so she can use a device to read his mind. They find her stabbed and Scotty doesn’t remember what happened.

They decide to use this lady’s powers to try to get to the bottom of it. She says words that no one understands. Thanks anyway, I guess

Then the lights go out for a few seconds and when they come back on the lady is murdered and in Scotty’s arms.

They get Scotty to a chair that can tell when he’s being honest. They find out it’s true that he has no idea what’s going on.

Through a series of questions, they find out that it was this guy, and that he’s Jack the Ripper, who was actually some kind of life-form that feeds on fear, and can cause people to be unaware of his actions with his powers. Yeah that would’ve been a tough one to figure out on their own

Kirk decides to give the crew some kind of drug that makes it so they won’t be scared. It makes sense, but also makes for a weird climax that we can’t take seriously.
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