I’m going to star creating pages like this for the various Trek shows, but the Original Series era seems to be one that people have most often asked me about, as it is now 60 years old and some people have a difficult time getting into it or seeing the point. There are 80 episodes of Star Trek: The Original Series. This is my list of what I’d call essential episodes, some of which I love and some of which I don’t. I’ll tell you which is which and why I think they’re worth a look.
TOS = Star Trek: The Original Series
TAS = Star Trek: The Animated Series
I should note that I list TOS episodes in production order, rather than airdate, as that is just how they make the most sense to me.
TOS Production #01 The Cage ****
The original Star Trek pilot, this story features an emotional Spock serving under Captain Pike with Number One (a then unnamed Una Chin-Riley), set 2 years before Discovery. Both Discovery and The Original Series feature sequels to this story and Strange New Worlds (featuring Pike, Una / Number One, Spock & an appearance by Medical Officer Phil Boyce on the Enterprise) is basically one big sequel to this episode. I’ve always loved this episode and was also always sad that we didn’t get more adventures featuring this crew, but thanks to Star Trek: Discovery and Star Trek: Strange New Worlds, we have! So what was for many years the unseen beginning of Star Trek has become an essential viewing experience. And I’ve always just loved it as it was.
TOS Production #04 Mudd’s Women *
I hate this episode but it features the return of Harcourt “Harry” Fenton Mudd as previously seen in DISCO S01E05 “Choose Your Pain”, DISCO S01E07 “Magic to Make the Sanest Man Go Mad” and Short Treks S01E04 “The Escape Artist”. The character returns later in this series (in a much better episode) and again in TAS.
TOS Production #07 The Naked Time ****
Terrific episode!
Events from this installment were revisited in Short Treks 2×04 “Ephraim and Dot” and there is a sequel episode in Star Trek: The Next Generation (S0103 “The Naked Now”). This episode also marks the first appearance of Christine Chapel since Star Trek: Strange New Worlds and it is later referenced in Star Trek: Lower Decks, so if you’re a fan of the newer stuff, this episode is essential.
TOS Production #08 Charlie X *****
One of the best episodes of Trek!
This episode features thematic ties to DISCO & SNW, notably, Spock playing three dimensional chess, plus the first TOS appearance of Spock playing his Vulcan Lute, and Uhura singing.
TOS Production #09 Balance of Terror ****
A great Trek episode, packed to the gills with cross series continuity.
The Federation comes face to face with the Romulans, finally revealing the historical ties between the Romulans and the Vulcans, which the audience has seen evidence of in both Star Trek: Enterprise & Strange New Worlds – but this is the first time the characters find this out. If that wasn’t enough, an alternate take on these exact events was dramatized in SNW S01E10 “A Quality of Mercy”, revealing how these events would have played out had Pike still been in command of the Enterprise, making this essential Star Trek viewing.
TOS Production #10 What Are Little Girls Made Of? ****
I’d say this is THE Christine Chapel episode of TOS. The episode also features Jim Kirk talking about his brother Sam along with the fate of Dr. Roger Corby, all of whom are featured in Strange New Worlds. Spock’s dislike of the term “half-breed” also falls in line with his backstory in Star Trek: Discovery (in which his sister Michael Burnham used this term to push young Spock away in a well-meaning attempt to save him from being associated with her).
The one moment that does seem like a continuity flub is when Christine asks Spock if he’s ever been engaged, when per SNW, she knows that he has – but she says this with a smile and in a sarcastic tone so it’s possible to interpret that she DOES know that he’s been engaged and that’s why she’s saying it that way.
TOS Production #15 Court Martial ***
This episode features Kirk being court martialed with several references that ties it to the excellent “Ad Astra Per Aspera” episode of Strange New Worlds (which featured the court martial of Enterprise First Officer Una – and remains my favorite episode of that series). That would be enough for me to enjoy it but it also features some interesting guest spots, my favorite being Joan Marshall as Areel Shaw, who is formidable, fair and a wonderful character who I would have liked to have seen more of.
TOS Production #16A The Menagerie, Part I ****
TOS Production #16B The Menagerie, Part II ****
The only two-part story of the Original Series era, this is the end of the road for Christopher Pike. A sequel to “The Cage”, these installments also serve as a sequel to Discovery’s S02E12 “Through the Valley of Shadows”, in which Captain Pike saw that he would one day face a horribly disfiguring accident, seemingly leading to a fate worse than death, as well as much of SNW, in which Pike has attempted to grapple with the fate he was shown. It may seem like the ending is already written, but DISCO / SNW fans should tune in to the end of the story before they jump to any conclusions.
TOS Production #18 The Squire of Gothos ****
Trelane, the trickster who was introduced in SNW S03E02 “Wedding Bell Blues” & returned in S04E07 “Like Chronitons Through the Hourglass”, returns again here and is given a name.
Before Strange New Worlds came along, many fans had long assumed a connection between this character and the Q (who appear in TNG, DS9, VOY, Lower Decks & Picard) but prequel series SNW actually intentionally implies it to be so, with Q actor John de Lancie voicing Trelane’s father – while also leaving everything vague enough so as not to spoil this episode. By extension, it is also possible that Trelane is Q2 / Q Junior, Q’s son featured in 2 episodes of Star Trek: Voyager (S03E11 “The Q and the Grey”, S07E19 “Q2”).
TOS Production #19 Arena **
A Gorn and a Metron are featured here after their arc in Strange New Worlds. I personally don’t love this episode, but if you want to see what inspired their somewhat bizarre story arc in that series, this is where it all began.
TOS Production #24 Space Seed ****
A hugely important episode on many levels.
This story features Khan and references to the Eugenics Wars, which were also explored in Enterprise’s Augments Arc: S04E04 “Borderland”, S04E05 “Cold Station 12” & S04E06 “The Augments”. The Eugenics Wars are why Stamets injecting himself with Tardigrade DNA was forbidden, tying this episode to Discovery. Khan was featured in SNW (S02E03 “Tomorrow and Tomorrow and Tomorrow”) and SNW main character La’an is a descendant of Khan’s. Khan and his followers return in 2 of the best Star Trek films: “Star Trek II: The Wrath of Khan” (1982) & “Star Trek Into Darkness” (2013). Fallout from the Eugenics Wars is key to a main character in Star Trek: Deep Space Nine and the events of this particular episode are revisited in Short Treks S02E04 “Ephraim and Dot”. A model of Khan’s ship is seen in Star Trek: Voyager Season 3.
Russian Weapons Officer Pavel Andreievich Chekov was not introduced until Season 2 of TOS, though a reference in “The Wrath of Khan” suggests that he was on the Enterprise during the events of this Season 1 episode.
TOS Production #27 Errand of Mercy ***
This installment is, retroactively, a sequel to the Enterprise episode S04E11 “Observer Effect”, which introduced the Organians, & Strange New Worlds S04E04 “A Case of Chiaroscuro”, which introduced Klingon Commander Kor (played by Demore Barnes). The Organians are later referenced in Star Trek: Prodigy.
This was the first episode of Star Trek to feature the Klingons and it specifically introduced John Colicos as Klingon Captain Kor, who returns in an animated series episode, “Time Trap” and 3 DS9 episodes as well. This also, retroactively, is the first appearance of the more human looking Klingons introduced in Enterprise’s “Affliction” / “Divergent” arc, which (again, retroactively) introduced Section 31. Kor is also featured in some Discovery comics (“Aftermath”) which help wrap up the second season of that series.
TOS Production #28 The City on the Edge of Forever *****
This episode is often cited as the best episode of The Original Series.
This story introduced The Guardian of Forever, which returns in what is ironically hailed as the best animated episode, “Yesteryear”, and is also later featured in Season 3 of Star Trek: Discovery, and is referenced in Star Trek: Starfleet Academy.
TOS Production #29 Operation — Annihilate! ****
The first season finale, this episode reveals the fate of Sam Kirk, Jim’s brother, who was featured in Star Trek: Strange New Worlds.