Totally with “City on the Edge of Forever”. It introduces the Guardian, which is figured in several Star Trek novels (including my favorite, Imzadi), and it also has Kirk/Spock rooming together for months at a time, Spock acting all jealous, AND - the best - I want to wear all the clothes. (♥)Best episode of Star Trek ever. Prove me wrong.i would have to say second best. tribbles all the way.
Plus, I kind of like Edith.

























