Summary

• "The City on the Edge of Forever" explores Captain Kirk's moral dilemma: love or duty.
• The greatest Star Trek episode centers on personal stakes with a no-win scenario and great sacrifice.
• Edith Keeler's death remains a riveting tragedy for Captain Kirk.

Star Trek: The Original Series' "The City on the Edge of Forever" is often hailed as the best episode of Star Trek, but what makes this classic time travel episode so great? In "The City on the Edge of Forever", Captain James T. Kirk (William Shatner) and Mr. Spock (Leonard Nimoy) chase a psychotic Dr. Leonard McCoy (DeForest Kelley) to 1930s New York City via the Guardian of Forever (Bartell La Rue), a sentient gateway to other times. Arriving too early before McCoy, Kirk and Spock are taken in by the 21st Street Mission, operated by Sister Edith Keeler (Joan Collins), a woman with boundless hope for the future whom Kirk falls in love with.

The crux of Star Trek: The Original Series season 1, episode 28, "The City on the Edge of Forever", written by science fiction author Harlan Ellison, is discovering Edith Keeler's death in a traffic accident has consequences for the future as the Starship Enterprise crew knows it. If Edith lives, her activism keeps the United States out of World War II, leading to victory for the Axis powers, and a future without the United Federation of Planets. Allowing Edith Keeler to die in 1930, however, means Star Trek's timeline is kept intact, but condemns the love of Kirk's life to an early grave. There are no easy answers, especially for a Captain who doesn't believe in no-win situations.

Why “The City On The Edge Of Forever” Is So Important To Star Trek

This Award-Winning Episode Made Star Trek's Time Travel Personal

"The City on the Edge of Forever" is one of the most important episodes of Star Trek. As a critical masterpiece, it won the 1968 Hugo Award for Best Dramatic Presentation, and a Writers Guild of America award for Harlan Ellison. It was named one of TV Guide's 100 Best Episodes of Television, and both William Shatner and Gene Roddenberry call "City" their favorite Star Trek episode. As a seminal Star Trek: The Original Series episode, "The City on the Edge of Forever" centers on Kirk's personal stakes in the moral dilemma. Edith matters to Kirk and the audience alike, so the human element becomes a template for Star Trek moving forward.

The Guardian of Forever returns, voiced by James Doohan, in the critically-acclaimed Star Trek: The Animated Series episode "Yesteryear", and is played by Paul Guilfoyle in Star Trek: Discovery season 3, episodes 9 & 10, "Terra Firma".

Later Star Trek series inherit the DNA of "The City on the Edge of Forever" with episodes using Star Trek's time travel rules, in which actions in the past have consequences for the future. Time-traveling Star Trek characters must blend in, and make difficult choices with personal stakes in the past. Notably, in Star Trek: Strange New Worlds season 2, episode 3, "Tomorrow and Tomorrow and Tomorrow", Lt. La'an Noonien-Singh (Christina Chong) loses the alternate reality Captain Kirk (Paul Wesley) that La'an loves, and keeps a young Khan Noonien Singh (Desmond Sivan) alive to ensure Star Trek's Eugenics Wars ultimately lead to the future's United Earth, despite the high death toll ahead.

“The City On The Edge Of Forever” Is Star Trek’s Greatest Episode

Kirk's Moral Dilemma Is Quintessential Star Trek

"The City on the Edge of Forever" is an unusual entry to top the lists of Star Trek's greatest episodes so frequently. There are no space battles or starships, and nary a Klingon in sight, but after all the expected Star Trek trappings are stripped away, what remains is quintessentially Star Trek. "The City on the Edge of Forever" asks Kirk whether loving Edith is more important than the existence of the Federation. It's the classic question of whether the needs of the many outweigh the needs of the few, and Star Trek's philosophy to prioritize the needs of the many is born with Edith Keeler's death.

With pure anguish, Kirk prevents McCoy from saving Edith's life.

And yet, Edith Keeler represents Starfleet's ideals of hope, compassion, and cooperation when these virtues are in short supply. Edith is us, the viewers, trying to make a difference now that gets us closer to the Star Trek future we want to see. Naturally, Jim Kirk and Edith Keeler are a great match, united in philosophy but separated by time and fate, but Kirk knows the stakes and actually accepts the no-win scenario. With pure anguish, Kirk prevents McCoy from saving Edith's life, and we feel the weight of responsibility with Kirk's heartbreaking sacrifice that makes "The City on the Edge of Forever" a Star Trek classic.

Star Trek: The Original Series is streaming on Paramount+.