I had to skip the bit where they use McCoy's great great granddaddy's gen-yoo-ine down south Patent Pending weed spray on the plant-dudes, because (surprise) their phasers are rendered inoperable.

I'm also not sure why cloning someone makes them ten times taller. Or drains the brain of the original. I suspect there's something a bit dodgy about about Keniclius's so-called "cloning" process.

Transcript

1
Captain's log, Stardate 5554.4. Exploring some new planet.
McCoy: Sulu's dying!
Kirk: What? How?
McCoy: He's an experienced botanist. He touched a poison plant!
2
Agmar: We are Phylosians, peaceful plant beings. We will save your friend.
Kirk: Thanks.
Agmar: We will now kidnap Spock.
3
Caption: Kirk has a fist fight with a plant!
SFX: Pow!
4
McCoy: Spock's dying. Something's happened to his brain!
Kirk: Again?
5
Keniclius: I, Stavos Keniclius 5, have cloned Spock! And drained the original's brain! We will ruthlessly enforce peace on the galaxy!
Kirk: But we already have peace. We did it... peacefully.
6
Spock 2: Kirk speaks logic. I will restore Spock with the Vulcan mind touch.
Sulu: Man, I feel like a good scrute.