"City on the Edge of Forever" is a notable episode of Friends written by Harlan Ellison. It was nominated for the Hugo Award for Best Dramatic Presentation in 1997, but lost to an episode of Everybody Loves Raymond.
Ross (David Schwimmer) and Chandler (Matthew Perry) are mistakenly sent back in time when Ross accidentally links the museum's atomic clock to the planetarium projector. The pair wind up in New York just before World War I, when peace activists are trying to prevent U.S. involvement in the European war.
Ross falls in love with a social reformer and anti-war activist named Fanny Zeiss (played by Jennifer Aniston), while Chandler runs afoul of a local fishmonger when he proclaims "Could it smell any more like rotting flounder?" outside of his stall. The fishmonger, Giuseppe Tribbiani (played by Matt LeBlanc), gets his aged mother (played by special guest star Sophia Loren) to curse Chandler, leading to a humorous run of bad luck.
Ross and Fanny's relationship develops and moves toward something serious, even though he knows it might change history if Fanny is distracted from her cause. But Ross also knows that he has to return to present-day New York, and tries to construct a crude time device based on the flux capacitor from Back to the Future. While pulling on a part for the capacitor, it suddenly lets go and causes Ross to hurtle backwards, where he collides with Fanny and sends her out a window -- that is seven stories above the street. Fanny is killed, as are the two anti-suffragettes she lands on (played by Courtney Cox and Lisa Kudrow).
Ross and Chandler then prepare to spend the rest of their lives in old New York, but are suddenly propelled back to the present thanks to Gunther, who broke the link between the atomic clock and the planetarium projector through a set of wacky circumstances that are only hinted at. Once home, they discover that Fanny's death was noted in the papers of the time as the loss of a "minor isolationist figure," but that the two anti-suffragettes she accidentally killed were key figures who could have blocked the 19th Amendment. Ross and Chandler try to claim to the rest of the friends that they were responsible for women getting the right to vote, but are rebuffed and made to pay for everyone's coffee.
Harlan Ellison has long disowned the final version of this episode, saying that the show's producers radically altered his script, which originally involved a drug-dealing crewmember, did not feature an Italian fishmonger, and most notably was not actually an episode of Friends.