Kirk gets wedged into a duel to the death with Spock. Never mind the circumstances of that - no one but the Vulcans are supposed to know. Anyway, Kirk forgets to check exactly what the duel is to, so of course he gets his ass kicked and dies.
No, wait. McCoy gave him something to simulate death and now he's all better!
This episode is the starting point for a fair amount of Trek fanfic, all of the Kirk/Spock variety.
"It has to do with... biology... Vulcan biology."
"You mean, the biology of Vulcans...?
-Spock and Kirk