#14: By Any Other Name
In case you forgot: Aliens from Andromeda have hijacked the Enterprise to help them conquer and colonize (in that order) the Milky Way. The Power Trio and Scotty defeat them with the power of being human.
The episode gets off to a strong start and keeps it up. The Power Trio comes up with a whole host of plans that meet with varying levels of success: getting a hold of the Kelvans' weapon, getting Spock on the ship, the suicide trigger, and finally convincing the Kelvans that they're better off in their alien bodies. While Kirk seems to be the most essential part of the puzzle on that last one—by seducing Kelinda and making Rojan jealous—everyone else on the ship who isn't a styrofoam polygon helps, too. McCoy gets one of the Kelvans hopped up on stimulants while Scotty drinks another under the table. Arguably those scenes are comic relief and filler, but they do serve a purpose. After all, the more experience the Kelvans have being human (as opposed to the galactic octopi they apparently "really" are), the easier it will be for them to accept Rojan's new mission: peaceful colonization with the help of the Federation.
But instead of giving the rest of the crew their due, it's another episode where Kirk saves the day with the power of his mighty mojo. I like that the humans and the Kelvans come to a diplomatic and peaceful understanding, without the use of any weapons, but it would have been immensely satisfying for drunk Scotty to hand over the alien weapon to Kirk to use against the Kelvans. Or, in a nice continuity nod, some of the humans get crazy psychic powers (remember how they crossed the edge of the galaxy in "Where No Man Has Gone Before"? And Kirk even references it in the episode!) and use those to immobilize the Kelvans.