"Wolf in the Fold"
Star Trek (the original series)
Much like "The Savage Curtain" was very nearly a Lincoln episode, "Wolf in the Fold" is pretty much a Jack the Ripper episode.
It's also a Scotty episode. By the second season, the original series began making a more concerted effort to focus on the supporting characters who would become well-known as part of the core group of the series (early in the first season, Nurse Chapel and Yeoman Rand were arguably more important than any of them, but then receded as the series progressed, and their significance in the films reflects that). This was of course Chekov's debut season, and he quickly stood out, even though he was an extremely odd choice for the reason his character was introduced at all.
(I mean, think about it: this mop-topped younger character was clearly meant to capitalize on the Beatles/Monkees...and yet Chekov wasn't British, he was Russian. You may, ah, remember, remember something called the Cold War? Which was still going on at the time? I think Chekov was really a passive-aggressive compromise in a show where Kirk was supposed to be the heartthrob. The producers want to introduce another one, but how to reconcile this competition with the series lead? Give him the wildly popular hairstyle. But yeah, make him Russian. Huge bonus points for looking past the present, as with the inclusion of Uhura, surely a mark in the show's ethnic profile, but still...Another reason, I think, that Star Trek had such a hard time finding respect. And you probably never even thought about that until now!)
Early in the second season they tried pushing Scotty as the would-be rescuer of damsels in distress, so he'd have something to do other than being a miracle-worker (isn't that enough???), so to then create an entire episode that casts him in the role of the quintessential threat against said damsels (hey, go back and read that parenthetical digression, on the off chance that you tend to ignore such things; although, catch-22, if you didn't read that one you won't be reading this one, now will you?) just goes to prove how little the producers tried to make sense of such efforts.
Which makes the fact that fans came to embrace Scotty, Chekov, Sulu, and Uhura to the levels they did, that there has been constant debate on how much of a jerk William Shatner is, strikes me as really quite startling. Because other than their regular appearances, these guys were clearly never near as important as Kirk, Spock, and McCoy.
Feel free to debate this. (You will be wrong.)