City on the Edge of Forever is without question the finest of the original Star Trek episodes, and rightfully has a place among the best science fiction of all time, small screen or large. The original script was written by decorated SF author Harlan Ellison, and the subsequent wrangling over edits and changes is the stuff of Star Trek legend. While what finally appeared departed somewhat from Ellison's costlier and more sprawling initial vision, it remains thought-provoking, harshly tragic, and deeply affecting.
We think of Captain James Kirk as the serial womanizer, romancing his way across the galaxy. And yet for all the loves in his life, the only one who ever competed with the Enterprise herself for primacy in his heart was Edith Keeler. And he had to let her die, for the future of humanity.
Through a convoluted series of events, Kirk and Spock are thrust into a 1930's America in the throes of the Great Depression, seeking a chemically imbalanced and furtive Dr. McCoy. All they know is that something McCoy did in the past changed everything in their present, centuries later. Through Spock's efforts in primitive computing, they discover the crux of the temporal problem - Edith Keeler. Edith, played with regal presence by Joan Collins, is a slum angel running the Twenty-First Street Mission, a homeless shelter and soup kitchen. She's a devoted pacifist, but also a futurist, convinced that mankind with overcome violence and hatred to blaze a path to the stars. Her vision and kindness and humanity resonate with Kirk, who finds himself falling in love with this unique woman from the distant past. Spock's researches reveal that in the altered timeline, Edith becomes so influential, and her message of peace and brotherhood so compelling, that America's entry into WWII is delayed, and the Nazis are able to conquer the world. In order to prevent this, and restore the "true" timeline, she must die as she originally did.
The result is agonizing for Kirk, who does not know when or where or how she is slated for death. In the end, of course, he plays the hero and grapples with McCoy in a half-tackle, half-embrace to prevent the restored doctor from saving Edith as an automobile runs her down in the street. It is one of the most tragic, heart-wrenching moments in television history, the bulletproof and swaggering captain holding on to his friend as he sacrifices the only woman he will ever truly love for a universe that will never know. But Jim does. When McCoy says, "I could have saved her. Do you know what you just did?", Spock's response, even in his flat, emotionless delivery, is devastating: "He knows, Doctor. He knows." In many ways, this moment is the one that cements the lifelong friendship, more than friendship, of these three people.
As is pointed out during the episode, the deeper tragedy is that Edith Keeler was right. She understood the future, she saw clearly that our acceptance of and compassion for one another is the only possible pathway to our collective survival. She was right, but too soon. It's a frustrating truth, that we know peace is the way, but too often fight and kill each other in staggering numbers in supposed pursuit of that peace. Will there come a day when we advance past our petty prejudices and our low greed? And will any of us live to see it?