Amok Time
Summary
When Mr. Spock begins behaving aggressively, Kirk discovers his first officer must return home to Vulcan to be married or die. Kirk disobeys his orders from Starfleet Command to visit Altair 6 and decides to save Spock. Spock, Kirk, and McCoy land on Vulcan where Spock takes them to his family land to begin pon farr. They meet T'Pau and T'Pring only to find that T'Pring wants a duel and chooses Kirk as a challenger. Kirk accepts the challenge thinking to let Spock win but is later told by T'Pau that it is a challenge to the death. During the fight, McCoy gives Kirk a neuro-tranquilizer to fake his death. Upon victory, Spock asks T'Pring to explain her decision and decides not to marry her. After beaming back to the Enterprise, Spock is overjoyed to see Kirk alive.
Summary from Wikipedia, CC BY-SA 4.0.
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