This was a fic posted on the KS Archive. Basically Earth is behind on technological development so Spock goes undercover to investigate. He runs into Kirk, his cover is blown, and he and Kirk get caught up in a conspiracy, and I CAN'T FIND IT!
I remember reading a story where Spock goes through Pon Farr and must mate or die so he rapes Kirk. He doesn't want to rape Kirk but he doesn't want to die, so he does.