#59: Tomorrow is Yesterday
In case you forgot: The Enterprise accidentally travels through time to late 1960s Earth and works desperately to undo the impression they fear leaving.
When you're dealing with science fiction, time travel is going to be a tempting (if not downright inevitable) plot point that comes up. This is the first such instance in Star Trek (discounting the last, weird ten minutes of "The Naked Time") and it was just as irritating upon rewatching as it was the first time I saw it. How could Spock (or the computer) fail to realize that captain Christopher would end up fathering the captain of the first successful Earth-to-Saturn probe? That seems like a pretty obvious oversight.
Shouldn't their encounter with a black hole-style anomaly have propelled them into the future, not the past? On the flip side of that coin, why does their "slingshot around the sun" idea send them forward in time instead of further into the past? If they've already messed with the timeline by taking Christopher aboard, how can they trust any of the history in the ship's databanks? More importantly, why does the Enterprise and everyone on it still exist? What if the Enterprise's visit to Earth is supposed to be part of the timeline? (And why doesn't Spock consider that last point?)
The logical consistency in this episode is just a big pile of NOPE.
The one redeeming factor is a little touch of melancholy at the end. It was Christopher's dream to go into space, and he got to do it, but he won't ever remember that he did. Kirk's runaround with the security is also pretty entertaining.