Out of the original seventy-nine episodes of Star Trek, one of the most respected and beloved is The City of the Edge of Forever. Written by Harlan Ellison the story is one of the more thoughtful and tragic in Trek Canon. It was also the first episode to feature a temporal plotline. Doctor Leonard McCoy (DeForest Kelley) accidently receives an overdose of medication and flees the Enterprise while in a delusional state. Beaming down to an alien planet he uses a temporal gateway (The Guardian of Forever) to travels back in time to earth during the Great Depression. By doing so he accidentally changes history. Captain Kirk (William Shatner) and Spock (Leonard Nimoy) follow him through the gateway to New York in hope of correcting the timeline. While awaiting the arrival of McCoy, Kirk falls in love with Edith Keeler (Joan Collins) who runs the 21st Street Mission. However he and Spock soon determine that to restore the timeline they must allow her to die.