The Enterprise is on approach to an alien world with the aim to establish diplomatic relations with it when it receives a message telling it to stay away. However, they are ordered by the Ambassador on board to ignore that message and find themselves drawn into a very strange war indeed.
Much of science fiction, especially Star Trek, aims to make comments on our own society and times via the activities of fantasy worlds. How well it manages to do that varies; it can be subtle and brilliant... or it can be like having a slice of lemon wrapped round a large gold brick applied to your head, to quote The Hitchhiker's Guide to the Galaxy.
Unfortunately this is a bit of a Gargle Blaster of an episode, intended as a commentary on the ongoing Vietnam War and coming across to me as one on the Cold War as well (remember this is five years after the Cuban Missiles Crisis) which comes across as heavy handed to me... also, a bit implausible. The central premise of the episode revolves around people willingly killing themselves because a computer has told them to do so. While I would agree that people have engaged in mass murder because someone told them it was the right thing, most humans do have a sense of self-preservation and surely some would have refused. Anyway, even the 'fake war' of the episode has real humanoid costs that would have an impact... and the length of time it has been going on is ridiculous. In short, the entire scenario falls apart at close examination.
Spock and Kirk don't have a great episode at all; Kirk is very unsubtle in his approach. The best of the crew is in fact Scotty, who refuses an order from Ambassador Fox that could get them all killed; reflecting a real incident in James Doohan's life where as an officer in the Royal Canadian Army, he refused to do something in a training exercise that would kill his own men.
Ambassador Fox (played by Gene Lyons, best known as the police commissioner on Ironside) is a complete and utter idiot; he clearly failed Common Sense. He ignores the message from the planet and overrides sensible decisions by the crew of the ship on the grounds of diplomacy, failing to realise (to quote Scotty) that sometimes the best form of diplomacy is indeed a fully armed phaser bank.
The planet is led by one Anan 7, played by David Opatoshu, a man with a suitably evil goatee and a slightly swarthy look that got a lot of roles as Middle Eastern characters over the years. He's clearly quite, quite insane. Apart from the guards in silly hats, the main other character on the planet is Mea 3, one of the few credited and on-screen appearances by Barbara Babcock (who mostly did uncredited voice work in the original series), who wears a classic female costume of this sort of era... or rather half one, which is pretty distracting.
The ending sees Kirk engage in some very reckless behaviour - basically risking a nuclear exchange between the two sides in order to force them to talk.
Finally, can we please stop these 'comedy' final scenes? They're getting irritating.
This is supposed to be a metaphor on the madness and stupidity of war. Unfortunately, it comes across as just stupid.