Star Trek: 10 Times Spock Abandoned Logic
7. Nearly Killing Kirk
In the Original Series' second season episode called Amok Time, Spock was gripped with Pon Farr, the Vulcan time of mating, and must return to Vulcan and marry his betrothed within eight days or he will die.
Defying a direct order from Starfleet, the Enterprise arrived at Vulcan where Kirk, Spock, and McCoy beam down. T’Pring and Spock are drawn together through their psychic bond to their marriage ceremony of koon-ut-kal-if-fee. It will be officiated by T’Pau, one of the most revered and respected Vulcans in history. However, T'Pring invoked the kal-if-fee, the right for her betrothed to fight for her and she chose Kirk as her champion.
Spock was so crazed with brain fever that he did something that he never would have done if he had been in control of his faculties, he killed his friend. In fact, at that moment, killing the Captain may have seemed the only logical thing to do. This was how far into the depths of Pon Farr Spock had fallen. But the realization of killing his superior officer and friend broke him out of his brain fever and he returned to the Enterprise to face murder charges. There, he finds Kirk alive and elatedly embraced him before collecting himself and returning to his previous stoic demeanor.