The Naked Time
A disease rapidly spreads through the crew, causing their hidden emotions and desires to surface as the Enterprise spirals towards a collapsing planet.
This is the first truly great episode, with one classic moment after another. The "character exposition disease" is brilliant, letting viewers see what these guys are really like. Some, like Riley and Sulu, provide great comic relief while releasing their youthful spirits. Nurse Chapel is more of a wet blanket than a hopeless romantic. Uhura and Scotty are not afflicted, but at least react to the epidemic in their characteristic ways, the engineer working his first miracles with a little help from Spock. As for the Vulcan, this is really his show. The briefing room breakdown scene is one of the most poignant of the series, with a powerful performance by Nimoy. Kirk's conflict isn't quite as compelling, though it's effective when he and Spock try to snap (and slap) each other out of their respective self-pity. A cure comes a little too easily, and the time travel method is not used again, though its an adequate metaphor for new possibilities.
Spock Saves the Day: The Vulcan stops the ship from spiraling towards the planet as Sulu leaves his post, then nerve pinches a crazed officer, and finally gives Scotty the formula for starting the engines cold.
Oops: Two words. Nervous breakdown.
Developments: Some very significant scenes found here. Spock's inner conflict, previously only hinted at, comes to the surface in the briefing room. The logical and emotional sections of his brain literally compete as he spurts out equations and confessions of love for his mother. Some insight into his upbringing is gained. Yet for all his anger, he longs most to express affection to those around him, and Kirk is there to hear his first declaration of friendship. Other "firsts" include his display of strength - he sends Kirk flying across the table with one hit! - and the more subtle nerve pinch. Longtime viewers will be familiar with Spock's essential characteristics, but this is a good refresher course. More than any other episode, it establishes Spock, in the words of Nimoy, as "a well-functioning pressure cooker."