Wink of an Eye
The Enterprise receives a distress signal, but finds no one on the planet's surface. They are in fact there, but move at speeds much greater than humans do. And they're about to give them a boost.
Actual science fiction! Good stuff. The accelerated planet is well conceived, and its people are a believable threat to the ship. Indeed, the takeover would be a success if Queen Deela didn't find Kirk so darn irresistible. (The "putting on the boots" scene is the best proof we have that Kirk ever got it on, and it's flimsy.) He does his bit in halting their plans, though Spock and McCoy are really to thank. All the speed-up/ slow-down effects are handled creatively, though those nitpickers will find inconsistencies. The buzzing noises, the manipulating of tapes, and the phaser fire are especially clever. Best of all, a peaceful solution is found, rather than the enemy being killed or allowed to die. As in the previous episode, the speed-up is a "super power" that would be useful in the future (witness Spock's repairs!) but is never touched again. Unethical? Maybe. Forgotten about? Most likely.
Spock Saves the Day: Does he ever! He's first to figure out - on his own - the nature of the Scalosians, and isn't afraid to down the water once McCoy has the antidote. At hyper speed he saves Kirk and overpowers the invaders. Then he repairs every system on the ship.
Oops: Risky move with the water, but not out of character.
Developments: While we're accustomed to careful experiments like Spock's examining of the tapes, the decision to drink the water is a reminder of the quick reasoning McCoy takes for recklessness. The Vulcan does like to surprise. Traveling at super speed is probably too cool to wait on.