THE INFINITE VULCAN
Written by Walter Koenig, no less!
This is the episode often derided for the 50-foot tall Spock but there are lots of really good sci-fi concepts featured here. At a minimum it does what season 3 had begun to – delving into already established areas of Trek lore and using that previous world building to tell new stories. Where else can you find reference to the Eugenics Wars with a peer of Kahn Noonien Singh himself; the master of cloning, Doctor Dr Stavos Keniclius! However, there's a twist – Keniclius , thought to be a tyrant like Khan is actually a champion for peaceful rule! Numerous references to continuity are offered up and Kirk again gets to espouse the enlightened future of the Federation.
We also get a historical lesson applied to the science fiction setting - Keniclius unwittingly spreading disease to a native race (I’m thinking Spaniards and Indians but there are probably many other examples). Then there's the whole notion of sapient plant life - a first for Trek (even if not an original concept in itself). The Phylosian alien design is creative and would have been utterly impossible for live action TOS. Equally so the impressive underground city. Having said that, those flying bat-plants are just crazy!!!
In fairness, there are some derivative elements from earlier episodes (Spock is captured because he’s the perfect specimen, has his mind removed as part of a master plan) but unlike
Spock’s Brain it isn’t the whole focus of the story and the mystery of Keniclius is given equal weight - not to mention the fact that his brain isn't physically removed
There's also Sulu, who picks up the unknown alien planet creature and nearly dies...Of course, this is from the same organisation that brought you idiots known to munch on borgia plants (
Man Trap) and drink Scalosian water without a second's thought. And speaking of
Man Trap Kirk states again here that he doesn’t like mysteries (I expect that they give him a belly ache and he has a beauty right now!)
In all, a good, meaty scifi story that also utilises various S3 elements and actually improves upon them
OTHER THOUGHTS:
- The episode begins with a standard exploration mission - good to see!
- McCoy is just as antagonist against plant aliens as he is towards Vulcans it seems.
- Not so Kirk who later recognises Agmar on sight (I must admit, the plant people all look the same to me)
- In the "tomb", we see that Agmar’s predecessors are huge! Going BTS this apparently was the reason why Keniclious made himself such large clones, in order to better interact with the inhabitants. IMO it's dialogue that really ought to have stayed in the final episode...
- Spock mentions that Agmar's people use almost 70% of brains – that old trope about humans only using a small portion of their brains pops up everywhere I go...
- The anti-weapon field is some great defensive tech, simple but effective – I wonder if it could be adapted to starships?
- The Phylosians are the last of their kind, as their “spore cells” have been destroyed. Couldn’t Keniclious just clone them? This is his master plan with Spock after all.
- Did McCoy really need to dig up his family weedkiller recipe? Isn’t there some far more efficient 23rd century equivalent?
- Keniclius mentions a war with the the Kzinti – I wonder who they are?
- Although he's done it to many computers, this is the first time that Kirk has talked a clone to death! (Well, to victory anyway)
- Kirk tries to subvert the whole “inscrutable Asian” sterotype with Sulu at the end there. The line is OK but it wins out against many S3 endings because it involves a character that is NOT Kirk, Spock or McCoy!
Go, TAS! 
