||The Enterprise visits a class M planet populated by a tribe of American Indians, apparently transported here from Earth in the distant past by an alien race. A giant asteroid is threatening to impact with the planet, and Kirk plans to divert it to save the locals. Although time is running short, the landing party take a few minutes to investigate a large obelisk on the surface of the planet. Kirk falls through a secret door and is blasted by a bolt of energy from a machine which renders him unconscious.
Spock and McCoy search for the missing captain, but with no sign of him they are forced to leave in order to intercept the asteroid on time. As the Enterprise heads out Kirk wakes and leaves the Obelisk, but he has no memory of who he is as a result of the energy blast. He is found by the tribe - they believe that the obelisk was created by the gods and Kirk's apparent association with it convinces them that he is a god.
The Enterprise intercepts the asteroid and runs the engines at maximum power in an attempt to deflect it. Unfortunately it's not enough - the ship's war drive is completely burned out, and the asteroid's course only minimally affected. All they can do is proceed back to the planet on impulse, hoping to find and rescue Kirk before the impact.
Meanwhile, Kirk begins to adapt to life on his new home. He falls in love with Miramanee, a local woman, despite the jealousy their relationship incites in her former fiance Salish. When one of the tribe's children drowns Kirk is able to revive him, convincing everybody that he has the power to bring back the dead and confirming his divine status. Miramanee conceives a child, and Kirk looks forward to a long and happy life with her.
As the planet begins to feel the effects of the asteroid's approach Kirk is called on to use the obelisk to send it away. When the tribe realise that he has no idea how to do this they turn against him, and begin to stone him and Miramanee. The Enterprise arrives and Spock beams down with a landing party, frightening the natives away. He mind melds with Kirk to restore his memory, and together they manage to find a way to open the obelisk. Spock deduces that the device is a massively powerful deflector system, and is able to work out how to operate it. The obelisk quickly diverts the asteroid, saving the planet. Unfortunately McCoy is unable to save Miramanee from her injuries, and she dies in Kirk's arms.
||Although the production values are high, especially for the low budget season 3, I never really liked this episode all that much. The "aliens visited Earth in the distant past" idea was already a cliche by this point, and it isn't really necessary here - the Indians could just as easily have been turned into an alien race without altering the plot otherwise. The setup seems a bit arbitrary - why is Kirk spending time on the planet at all if the rendezvous with the asteroid is so critical? Surely investigating the obelisk can wait until after the diversion, when you have all the time you need.
Kirk falls in love once again, and I must say this is one of the more convincing relationships he has since the plot allows the time for it to develop properly. It would have been interesting to have Miramanee survive and leave with Kirk, but I guess 60s TV wasn't really ready for a captain with a wife (for that matter, we've never seen the "hero" captain with a wife in any incarnation of Trek. Only Sisko comes close, and she was dead when we first saw her!)