Great episode: A transporter accident mixed with some kind of electric phenomenon switches the minds of Kirk, Uhura, McCoy and Scotty (I think I got them all) with the minds of their alter egos in some crewed up alternate reality (and not their bodies since they're wearing the other people's costumes) where most every one is a selfish evil bastard (even the women). This will be known henceforth as the Mirror Universe. Mirror Spock is a bit of a hard ass but to his defense he's one of better ones, or less evil ones if you will. After tasting the joy of being in a world where most of the people surrounding you are potential traitors. Our little group find a way to put things back to the way they were but they're almost stopped by Alt-Spock who finally lets them go after Kirk has planted in his mind the seed of dissent.
Turnabout Intruder
Turnabout Intruder