The Arizona town of 1881, recreated in fragmentary form by the Melkotians as the place of execution for Kirk's landing party, who are cast as the losing side at the OK Corral.
Tombstone is the setting of most of the original series episode Spectre of the Gun. After Kirk ignores a Melkotian warning buoy, the landing party is condemned to die in a surreal, half-built version of the town drawn from Kirk's own knowledge of American frontier history, on 26 October 1881.
Kirk, Spock, McCoy, Scott and Chekov find that the townspeople see them as the Clanton gang, destined to be shot by the Earp brothers and Doc Holliday at five o'clock. Attempts to leave are blocked by a force field, and Chekov is apparently killed in a quarrel over a local woman, Sylvia.
Spock concludes that nothing in the town is real and uses mind melds to make his companions certain of it, so the Earps' bullets pass harmlessly through them. Kirk's refusal to kill Wyatt Earp impresses the Melkotians.