Balance of Terror
Kirk chases a Romulan ship across the Neutral Zone and finds their captain an intelligent opponent with distinct advantages, like a cloaking device.
Here is proof you don't need astounding special effects to create a gripping space battle. In fact, the visuals are even worse than usual: phasers looking like torpedoes, the Enterprise is black & white, red blocks attacking; no wonder the warbird was kept cloaked! But good writing and a powerful performance by Mark Lenard (later to appear as Spock's dad) make this an exciting ride. Kirk makes some real moves instead of his usual bluffs and cheats, and the Romulans prove just as clever. Kirk also battles bigotry as suspicious eyes fall on the pointy-eared Spock. The wedding plot is a little melodramatic, but upholds the first season tradition of showing the crew's personal lives as well as their professional duties. Highlights of the battle scenes are the nuclear warhead detonation and the best "crew flies across the bridge" shot yet. The Enterprise finds its victory hollow, since the young navigator is dead and the Romulans' death regrettable. Even more so than The Corbomite Maneuver, this episode affirms that for all its weaponry, Kirk does not command a war ship.
Spock Saves the Day: Spock advises attack, repairs the phasers, launches them, and rescues several officers from a deadly purple haze.
Oops: Watch those switches! Even Vulcans fumble, it seems.
Developments: Spock reveals a bit of history: that the Romulans are offshoots of Vulcans who rejected their dedication to logic. He's quite tolerant to those who suspect a more current connection, like Stiles. With patience and reason, and by being in the right place at the right time to save the lieutenant's life, Spock wins Stiles's respect. Interestingly, Spock spends the late years of his life undercover on Romulus working for reunification with Vulcan. In an unrelated "Huh?" moment, it's unclear whether the Vulcan is able to break the cast rodinium because of his strength or because the shielding was weakened by the attack. I suspect the latter, but with Spock we can never be sure.