TOS Season One, 1967
#18 Jan19 Arena
#19 Jan26 Tomorrow is Yesterday
#20 Feb02 Court Martial
#21 Feb09 The Return of the Archons
#22 Feb16 Space Seed
#23 Feb23 A Taste of Armageddon
#24 Mar02 This Side of Paradise
#25 Mar09 The Devil in the Dark
#26 Mar23 Errand of Mercy
I should also note that I am using air-date as the criterion of "sequence", and that Amazon Prime's sequence numbers are also indexed to that, and as such do not correspond to any official "episode numbers" nor "production numbers" such as are found on http://en.memory-alpha.org/wiki/Star_Trek:_The_Original_Series.
#19 Tomorrow is Yesterday, 1/26/67
This episode always struck me as having the most deceptive of cold opens -- footage of a current-technology fighter jet, supposedly scrambling to investigate a UFO, which we only learn at the very end of the teaser is, cue the theme, the Enterprise. Almost as if Roddenberry were trying to hook new viewers of a military bent.
Of course, for science fiction types, it's a giveaway that we're going to have a time-travel episode. And sure enough after the intro, we find the Enterprise crew reeling from some interaction with an undetected "black star" and soon realizing from a radio broadcast that they've time-travelled to the late 1960's. What a coincidence. The whole first part of the exposition here is really bad -- they can't detect black holes in advance in the future??, Kirk has no idea of the potential stress to the jet of ordering the "tractor beam"??, captain Christopher transports from a sitting to a standing position??. Little better is the contrast and contest of competency between the two captains (and two cultures). Kirk does the whole smarmy male-dominance welcome-aboard-I-know-more-than-you dance, while Christopher does the name-rank-serial-number bit, ogles a female crewmember, makes digs about Kirk's "accidents", but "can't deny the fact that you are here" (uhh thanks). This is all punctuated by a trip in the turbolift where they hold their ... down-facing turbolift controllers, of course. But quality improves rapidly as Spock becomes involved.
Starting immediately upon first contact: Christopher: "I never have believed in little green men." Spock: "Neither have I." Heh. Christopher's whole unspoken reaction of "WTF, well I guess he isn't "little" is well done. Spock also introduces the whole moral/time paradox of whether Christopher can ever be returned, due to now knowing "the future".
Then, wow, the whole scene in Kirk's quarters to end Act One is excellent. The misbehaving computer is a real gem, popping the whole male-dominance balloon, and giving Christopher another chance to dig at "future problems". Countered by Kirk and Spock double-teaming him on not being able to go home, to which he reacts with a foreshadowing reference to his family. And finally ending in the stalemate, maybe I can't go home but neither can you. Touché.
Act Two sees Christopher's attempt to commandeer the transporter to return, defeated by Kirk's fists. And we're back into macho mode -- Kirk even put the computer back in it's place, and Christopher, now in sickbay, does the whole admiring bro-code "I see they have physical training in the future too" business. Again it is Spock who saves the scene, first with a true-scientist's admission of an error earlier, then with the "news" that although Christopher makes no relevant contribution to history, his future son does. The whole "I don't have a son"/"not YET" is a nice dramatic touch, but the dreamy "I'm going to have a SON" business is gratuitous and out-of-character. And, you know, the wife is kinda-sorta-gonna have something to do with that too (should have been "we're", eh?).
Next is the stealth scene where Kirk and Sulu attempt to recover/destroy evidence on the base of the existence of the Enterprise. It adds some nice suspense, although Kirk's dallying to admire a bulletin board and trophy case makes no sense. This (and the one later) is also a rare (only) scene with Takei and Shatner alone; the lack of chemistry is evident. The scene and act end with another comic relief, the security guard getting beamed up. This may be the first instance of an "alternate use" of the transporter, so well spoofed in Star Trek 2009 (trans-warp beaming). And this episode has more comic relief than I remembered (joining The Trouble With Tribbles, I Mudd, and A Piece of the Action).
Act Three is Kirk and Sulu being caught yet again on the base, Sulu escaping with all the recovered evidence, Kirk demonstrating how many men are required to subdue him (three) and how to avoid being interrogated, Spock, Sulu, and Christopher coming to rescue Kirk, and Christopher yet again trying to escape afterward, foiled by the Vulcan pinch.
Act Four is exposition and enactment of the "slingshot" worked out by Spock and Scotty that will return the Enterprise to its time after conveniently allowing the return of Christopher and the guard to the previous day (with somehow no Enterprise nor crew appearing then any more). Kudos to the remastering team though for distracting from some of that malarkey by some great new Earth and Sun effects.