TOS: Space Seed (w/Khan). My stepdaughter and I had seen ST2 recently and we both wanted to see the TOS episode that had preceded it. It was a good episode though I did wonder why Khan didn't try to take the Enterprise again after Kirk had foiled his attempt and accepted resettlement of him and his crew on Ceti Alpha 5 relatively passively. Also, I wonder why exactly Kirk didn't think that leaving him on Ceti Alpha 5 might end up becoming a problem eventually (as Spock observes), at least without some kind of Federation supervision? They would've had to realize that a group of malevolent genetically-engineered might eventually figure some way to get off the planet and cause trouble for the Federation (which they ultimately did). OTOH I'm not sure what other options Kirk might have had other than retrieving the Botany Bay and sending them back into stasis- though I'm not sure that would've worked. I guess sometimes there are no perfect solutions to difficult problems like that.