The Enterprise is accidentally thrown backward in time to 20th Century Earth, just days before the first mission to the Moon, where it is picked up and pursued by the Air Force as a UFO. Ironically, this episode first aired on January 26, 1967, just one day before the Apollo One fire, an event that took the lives of three astronauts and delayed the real missions to the Moon.
We learn that, much to the annoyance of Kirk and Spock, the ship's computer has a female personality. This was part of an attempt to add some humor to the episode but it didn't work (It's really much more degrading to women). There's just one moment for me that was funny. Kirk is explaining the situation to Christopher after he beams aboard. Just as they walk onto the bridge Christopher says "I never have believed in little green men" as Spock is revealed saying "Nether have I." Unfortunately, this is the highlight of the episode.
Once they have recovered the films and realize that by not returning Captain Christopher they will be altering history, Spock and Scotty devise a plan to make everything right again. Spock explains it to Captain Christopher, "the only possible solution is the slingshot effect, like the one that put us here. My computations indicate that if we fly toward the sun, seek out its magnetic attraction, then pull away at full power, the whiplash will propel us into another time warp....Logically, as we move faster and faster toward the sun, we'll begin to move backward in time. We'll actually go back beyond yesterday, beyond the point when we first appeared in the sky. Then, breaking free will shoot us forward in time, and we'll transport you back before any of this happened."
Um, okay. Kirk adds, "You won't have anything to remember, because it never would have happened."
Next up, will be a classic Kirk vs. Computer episode - Return of the Archons.