The City on the Edge of Forever ()
Kirk and Spock must travel into the past in order to correct a change that will alter history.
While the USS Enterprise orbits an unexplored planet, Chief Medical Officer Leonard McCoy treats an injured Lt. Sulu. When the Enterprise is rocked by a time distortion, Mccoy accidentally injects himself with an overdose of cordrazine, a dangerous drug. Delusional and paranoid, McCoy flees from the bridge to the transporter room, beaming himself down to the planet below. Captain James T. Kirk (William Shatner) leads a landing party to look for McCoy. They come across an ancient glowing stone archway, which turns out to be the cause of the time distortions. They discover the archway to be sentient. This “Guardian of Forever” explains that it is a doorway to any time and place. While Spock records historical images from the portal, McCoy escapes through it. The landing party suddenly loses contact with the Enterprise. The Guardian informs them that McCoy has altered the past; the Enterprise and all they knew are gone.
The Guardian permits Kirk and Spock to follow McCoy to repair the timeline. Spock times their passage to arrive where McCoy did ahead of when he will arrive, and they find themselves in New York City in 1930, during the Great Depression. After stealing clothes from a fire escape to blend in, they meet a woman named Edith Keeler (Joan Collins), who runs the 21st Street Mission. They are given a place to sleep, along with doing odd jobs to earn money. Spock works to devise a method of interfacing with his tricorder and analyze its recorded images to determine how McCoy has altered history. While they await his arrival, Kirk and Keeler spend time together, and Kirk begins to fall in love.
McCoy arrives and stumbles into the mission, unnoticed by Kirk and Spock, and Keeler nurses him back to health. Spock completes his work and discovers Keeler was supposed to die that year in a traffic accident. Spock learns that Dr. McCoy altered the past by saving Keeler’s life. In the altered timeline, Keeler founded a pacifist movement on the eve of World War II. This causes the United States to delay its entrance into the war, allowing Nazi Germany time to develop nuclear weapons, launched in their V-2 rockets to conquer the world. Kirk admits his love for Keeler, and Spock answers that Keeler must die to prevent millions of deaths and restore the future.
Going with Kirk to see a movie, Keeler mentions McCoy. Kirk, shocked and excited, tells her to stay where she is and calls Spock to tell him this. The Starfleet trio reunites in front of the mission. Observing this and curious, Keeler crosses the street to join them, and she steps right in front of a fast-moving truck. Kirk turns to save Keeler from the truck, but a shout from Spock freezes him in his tracks. Then Kirk blocks McCoy from saving her, and she is struck and killed. Not knowing why Kirk and Spock did what they did, McCoy is stunned and in disbelief that Kirk had knowingly stopped him from saving Keeler.
Kirk, Spock, and McCoy are returned to the Guardian’s planet. The rest of the landing party is waiting with history restored. When the Guardian declares that “many such journeys are possible,” a brokenhearted Kirk simply states, “Let’s get the hell out of here.” The landing party beams off the planet back to the Enterprise.