6. Amok Time
When Spock seems on the verge of suffering an emotional breakdown, Kirk and McCoy learn that he is going through pan farr, a physiological condition occurring in Vulcan males every seven years. Spock must return to his home planet and take a wife. In Amok Time, audiences got a peek at the planet Vulcan for the first time, and the culture and customs of the galaxys most logical race are explored. Much of Trek lore came to be in this episode, particularly as it pertains to Vulcans and their hot, arid planet. Credit is given to Leonard Nimoy himself for developing the Vulcan salute. Amok Time highlights the relationships shared by the series three main charactersKirk, Spock and McCoy. While suffering the effects of pan farr, we glimpse Spocks human, emotional side: his capacity for anger, his genuine affection for McCoy, and his grief at having killed Captain Kirk. When Kirk turns up alive at the end of the episode, Spock is so overcome with joy that for a brief moment he loses his Vulcan mask altogether.
Memorable line: "What they are about to see comes down from the time of the beginning, without change. This is the Vulcan heart. This is the Vulcan soul. This is our way." - T'Pau