WARNING: This thread WILL contain unhidden spoilers for this entry. Because this re-watch is in a slightly-subjective chronological order and not in production order, please refrain from talking about the content of other episodes or movies in this thread. If you do, please put that content inside spoiler tags. Some people here may be watching Star Trek for the first time.
#52: Star Trek: The Original Series, season 2, episode 22 "By Any Other Name"
Written by D.C. Fontana & Jerome Bixby, directed by Marc Daniels.
Stardates 4657.5 through 4658.9 (August 2268)
"To use this ship, you have a to use our form." - Captain Kirk
Captain Kirk beams down to a lush planet with an away team to track down the source of a distress call. Out from the trees emerge two humanoids with expressionless faces who confidently announce to Kirk that they will take over his ship. The moment Kirk begins to protest, the aliens freeze the entire landing party in place with some sort of device. The y are held captive on the planet while more of their kind materialize on the Enterprise through the shields and systematically take over the ship. They are Kelvans from the Andromeda galaxy. They crashed in the Milky Way galaxy when their scout ship passed through the galactic barrier and they need the Enterprise to return home - a 300-year journey across the void between galaxies.
Originally released: 23 February 1968
"By Any Other Name" on Memory Alpha (mirror)
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What did you think?

This was one of the few TOS episodes I saw growing up, and one of my favorite among them.
Once again, poisoning the enemy with humanity. Forcing an otherwise superior race to navigate primal behaviors that humans simply grow up learning to manage.
And Scotty drinking his minder under the table is the best part of the episode. The bagpipes that keep playing during those scenes are so appropriate to Scotty's resolve they're almost not racially insensitive. So good, that the The Next Generation calls back to it 25 years later.
Spoilers for Star Trek II: The Wrath of Khan
Watching episodes like this one after learning about how Kirk never truly faced death gives Shatner's overacting here a whole new layer to it. He simply cannot accept what is happening and almost completely shuts down when someone is casually forcing him to endure loss.Also, what kind of guilt trip did Lieutenant Shea have when he realized he was the only one brought back?