10 Star Trek Moments That Broke Our Hearts
5. He Knows, Doctor. He Knows.
Edith Keeler must die.
Yes, that's a harsh way to begin this entry, but her fate was always sealed. It was the avoidance of this fate that spelled doom for Starfleet and the Federation - her pacifism saw the delay of the United States' entry into the Second World War, thus allowing the Axis forces to prevail. Dr. McCoy, in his constant attempts to save human life, ended up creating a dark version of reality - all because of his heart.
For McCoy, though, the pain that he would surely have felt at the knowledge he had undone the birth of the Federation was spared. Spock and Kirk traveled, via the Guardian of Forever, to a point slightly further back in time, and were able to set things right. By setting things right, they were forced to involve themselves in the events of the time. Though cliched for sure, this included Kirk falling in love - with Keeler. Perhaps a betting man could have called it, but it is how things are handled that lands it a spot here.
The version of The City On The Edge Of Forever that made it to screens may be vastly different from Harlan Ellison's original script, though the devastating ending has never lost its true impact. The elation that Kirk, Spock, and McCoy share for the briefest of moments only makes the blade of Keeler's death all the more piercing - particularly as Kirk has to hold McCoy back from saving her. The Doctor doesn't understand why Kirk has done what he has, so we as an audience watch his face fall from joy to panic to horror - all in mere moments.
It is Spock who must assure him that Kirk is well aware of what he had to do, for the latter is too broken to say anything at that moment. This episode remains as powerful today for many reasons, not least of which being the brilliant use of the tragedy of time travel. Kirk could never have stayed with her. He simply didn't realise how directly involved in her death that he would become. With bruises running deeper than ever before, he leaves the planet, and Star Trek was changed.