Spectre of the Gun

When the landing party beams down they meet a Melkotian, who informs them that their tresspass on his planet is punishable by death. Kirk, as the leader, will be used to supply the "pattern" of their death. In an instant the officers find themselves in a strange recreation of a 19th century town of Earth's "Wild West". Missing their equipment, each is carrying a gunbelt of the period. The inhabitants refer to the officers by the names of the losing participants in the infamous "gunfight at the OK corral". It seems that the Melkotians have recreated the incident in order to provide suitable deaths for the Enterprise crew.

Kirk struggles to convince the locals of his real identity, but is dismissed. He resolves to find some way to defeat the Earp brothers without engaging them in a gunfight; McCoy and Spock build a gas grenade which should incapacitate their opponents. Whilst they are working on the device, Chekov gets into a fight with Morgan Earp and is shot and killed - since Chekov's character William Clairborne survived the original gunfight, this proves that events are not predetermined to go as before.

The grenade is completed, and Scotty volunteers to be a test subject. However, it fails to have any effect on him. Only Spock realises the profound nature of this - the grenade must work, by the very laws of science which define reality. If it does not work then those laws are not operating, and there is no reality. Spock concludes that nothing around them is real; the entire scenario is a telepathic construct created by the Melkotians. Kirk notes that whilst Spock may be able to use pure Vulcan logic to dictate his beliefs, the Humans will inevitably harbour some doubt about his conclusion - and that doubt may be enough to kill them if they are shot in the illusion. With time running out Spock mind melds with each officer and convinces them that their situation is purely illusion. The group stand calmly whilst the Earps fire straight through them, then defeat them in a fist fight.

The illusion ends, and the party find themselves back aboard the Enterprise - including Chekov. The Melkotians, pleased that Kirk chose a non-lethal approach to solving his dilemma, offer to establish formal relations with the Federation.

The biggest achievement of the episode is in making good use of the show's micro budget. They couldn't afford proper sets for their western town, so they just left large areas of the buildings missing and used it as a point of the plot, a way to show that the characters are in a surreal environment constructed for them. It works very well.

Another favourite element of mine is Spock's solution to the problem. His reaction to the gas not working is practically the definition of rationality - reality cannot be this way, therefore this cannot be reality. It always struck me as being a very profound moment, and Nimoy delivers it extremely well.