This episode is the first ever appearance of the Klingons, who would become a major part of the Star Trek universe. In this incarnation, the Klingons were portrayed as what now appears to be an almost painful "Yellow Peril" stereotype, who would only later evolve into the Proud Warrior Race of later movies and series. In this episode, Kirk threatens one of the subordinate Klingons, who promptly and cowardly spills his guts (figuratively; literally would actually be appropriate for later Klingons).

One of the cool things about this episodes is that when Kirk and Spock beam down to Organia we see the locals and some farm animals, which include bright green goats. But as we discover later, the Organians are actually beings made of pure energy, and everything on their world is merely a construct of their minds. One must conclude that they like their goats to be green for some reason.

Transcript

1
Captain's log, Stardate 3198.4. Negotiations with the Klingon Empire have broken down. En route to Organia to prevent Klingons occupation.
Spock: Organia is a primitive, friendly society.
Kirk: They clearly need our help defending their planet. In exchange for white rice.
2
Ayelborne: Welcome, visitors.
Kirk: I need to speak to someone in authority.
Ayelborne: There is no authority.
Kirk: You'll do, then.
3
Kirk: The Klingons will occupy your planet.
Ayelborne: We do not need your help.
Kirk: Can you explain why?
Ayelborne: No, we will keep being interrup—
Sulu: {over communicator} Klingon ships approaching, captain!
4
Kirk: Get out of here, Sulu! Contact Starfleet for reinforcements.
Sulu: Weren't they already sending more ships?
5
Kor: I am Kor, your new military governor.
Ayelborne: Welcome.
Kor: You welcome your conqueror? You snivelling bunch of—
Ayelborne: Does that make you angry?
6
Kirk: I am Baroner, a citizen of this world.
Spock: And I am Spock, a trader in kevas and trillium.
Kor: A Vulcan! Interrogate him with the mind-sifter!
7
Kirk: You need to fight back!
Ayelborne: No we don't.
Kirk: Why?!
Ayelborne: Because—
Kor: Here's your Vulcan back!
8
Kor: His mind is too strong. But you, Baroner, I can peel your mind and leave you a vegetable.
Ayelborne: No need. He is Captain James T. Kirk of the Federation.
Kor: A-ha!
9
Kirk: Don't you know anything about withholding information from the enemy?!
Ayelborne: There is no need, Captain. As we've been saying, we—
Kor: Enough! Lock them up!
10
Caption: Kirk and Spock escape:
Kirk: It's up to us to save this planet of peaceful farmers.
Spock: Like some sort of... Space Cowboy?
Kirk: Where's Robert Vaughn when you need him?
11
Kirk: Right, Klingon scum! Now we fight!
Ayelborne: No, you don't. We are actually omnipotent god-like beings who deplore violence. You will make a truce.
Kirk: Oh, that's a nice change. <cough>Metrons<cough>
12
Ayelborne: You and the Klingons will be friends in the future.
Kirk: I doubt it.
Ayelborne: And the next Enterprise captain will be bald and drink Earl Grey tea.
Kirk: Now I know you're joking.