Sulu touches a little walking plant and is gonna die from its poison

But then some plant aliens show up and cure him

They show them their dead relatives. A human came to this planet and inadvertently brought a plague with him.

Then some flying plant things show up

There communicators and phasers stop working. It was a trap!

The plant things wrap everyone up and force them to make weird expressions

And they take Spock!

Then a giant clone of the human that came to this planet shows up. He says he’s taking Spock and the rest of them should scram

They look him up and find out he was involved in the Eugenics War, and he wanted to make super people through cloning

Kirk, Bones and Sulu go back to the planet and find a plant to question.

They figure out where Spock is, but he’s already been cloned

When the plants attack again, they use weed killer developed by Bones’ great grandpa, who apparently was a bit of a gardener.

The original Spock will die! His mind is fading away due to the cloning process

Kirk tries to reason with the giant Spock, reminding him about IDIC and all that stuff

So giant Spock does a “vulcan mind touch” to restore his mind

They find out that the original human actually wanted to make clones to act as a peace keeping force. Kirk explains that they already got peace, so they should give the original Spock back. So they just leave the giant Spock to hang out with this guy and his plant people.

One of the many odd lines from this episode: “By the way, Mr. Sulu, any chance of teaching me that body throw? Could come in handy some time.”
“I don’t know, sir. It isn’t just physical, you know. You have to be inscrutable.”
“Inscrutable?!? Sulu, you’re the most scrutable man I know!”