 The Enterprise finds on its path a sophisticated buoy, placed by the highly advanced Malcotians, who make clear by telepathy to have decided their territory was encroached upon, so the ship is forced in orbit, and the  intruders  considered a  disease  which must be destroyed. A landing partner comprising Kirk, known to be in command, Spock, McCoy, Scott and Chekov is sentenced without trial. They find themselves in a recreation of Tombstone, Arizona in October 1881, the site of the fight at the OK Corral, apparently to die according to the pattern of ancestral violence the Malcotians copied from Kirk s mind, casted as the Clanton clan which opposed the Earp family and got exterminated- can history be changed in this reenactment? The crew is still in its own uniforms, so Kirk tries to avoid the fatal fight by talking sense and denying to be Clantons, but they are still given a five o clock ultimatum. A forcefield prevents them from leaving town, so they decide to prepare tranquilizers to fight without killing. Alas Chekov is friendly to responsive local girl Sylvia, and gets shot by Wyatt Earp- dead, unfortunately but as Spock points out clear proof the outcome is not preset. Kirk mistrust everything now, so they test the tranquilizer on Scotty- it has no effect, which is scientifically impossible. The forcefield pinpoints them to the fight-scene at the corral. Spock concludes the suspension of physical laws imposes a crucial conclusion...