"The City on the Edge of Forever" Season 1, Episode 28. My favorite episode. By far. Introduces the Guardian of Forever, time travel, and the whole idea that "Edith Keeler must die" is, frankly, the best set up for a show ever. No saving everyone in this episode. Harlan Ellison wrote this episode. The best ending line of the show too, with Kirk saying, "Let's get the hell out of here." With all the apocrypha and changes that have been documented and rumored, as this episode is finished, it is by far the best of all Star Trek. Hands down. The argument could be made that any science-fiction show could do this episode as you really don't need these specific guys, but taken as a whole, it helps us understand the relationships of these three crew members, as Spock has some wonderful time on camera, and Kirk does what he has to do. This planet that the Guardian is on would be classified as even more quarantined than Talos IV. Indeed, there is the...