This one really is one of the all-time Trek greats - one of the best episodes of the first season and, for that matter, of the whole three years of the series. It begins as a mystery on a very peaceful planet, where settlers were meant to begin an agricultural colony several years ago. Kirk tries to unravel this odd jigsaw puzzle presented before him in the first act - the colonists should all be dead by this point due to what are known as Berthold Rays and all animals have indeed died off. The answers lie in some funky-looking plants which shoot spores into human beings, thereby indoctrinating them into a space-age version of a 'happiness pill' society. All worries melt away and humans can, for the first time since Adam & Eve (one might say), relax in paradise. In a sense, this is "The Naked Time" episode taken to the next level - rather than fighting a form of disease, mankind here seems cured of all ills - there appears to be no reason to escape something so benevolent.
There is a beguiling quality to most of this episode and moments of incredible poignancy. Most of these moments are in Spock's scenes, usually with his newfound lady love (the luminous Ireland). Here we see Spock as perhaps he really is without that wall of anti-emotion he projects - this story hints that it really is an artificial wall, even unnecessary. This is not Spock afflicted by sickness or possessed by an alien force - it's the real Spock, smiles and all, all his usual defense mechanisms swept away, as human as, well, Dr. McCoy. Swept Away - that's probably as good a description as any for what happens to him and then the rest of the crew. And ironically, it's most tragic for Spock, among all the crew, when this happiness is taken away - we realize he loses the most here - everyone else just realizes they've been kind of wasting their time. Interestingly, Kirk proves to be the only one resistant to these spores, to a degree. I guess that's why he's captain - it takes a lot more to dissuade him from his mission than it does the average crew member.
Overall, this episode presents a superlative progression of surprise, suspense and some jarring thrills following on the heels of the early mystery. After Spock gets through that brief, though alarming, painful transition to his new self, we see Kirk's astonishment as he first observes his transformed first officer (more irony here: Kirk could have really enjoyed a relaxed friendship with Spock if things continued as they were here, a typical 'best friends' relationship, though McCoy might've gotten jealous and then burned off the effect of the spores). Then the ship empties; this was the first time something like this happened - now things look really grim - and once Kirk exits, that's it; the ship will burn up in a decaying orbit. I believe this episode has the shot of the empty bridge which was later used in the TNG episode "Relics." Those hints we've seen of Spock's Vulcan strength prove to be quite valid - don't ever anger a Vulcan, especially if you're a frail human. I don't pretend to understand all of Kirk's insults but I think his reference to freakism did the trick. Finally, McCoy gets in the best line towards the end when he tells the colony's leader to make him a mechanic - "Then I can treat little tin gods like you!" Priceless.
