 The Enterprise in attacked by a missile, launched from an asteroid on an independence collision course with highly populated planet Darren 5 in 396 days, which has simple atomic power and an internal atmosphere, but no inhabitants. McCoy has found he s the only unhealthy crew member: only one year life left. Kirk, Spock and McCoy beam down to the asteroid surface but are suddenly overpowered by sword-bearing men, commanded by high-priestess Natira who makes them kneel before a worshiped oracle, which smites them down electrically. They are given a medicine by an old servant who suffers pain twitches while telling he once saw the forbidden world outside and dies. The earthly visitors are now offered hospitality. The high-priestess asks McCoy to stay as her mate and explains the people is on its way to a new, green world,  soon  according to the oracle. Kirk and Spock discover the oracle was build by the alien Fabrini civilization, this people is oblivious they are on a space-ship which will collide. They overhear the oracle tell Natira her mate must accept the instrument of obedience, then it smites the duo and orders their execution; McCoy convinces Natira to spare their lives if he stays as her spouse; Kirk and Spock beam up. McCoy gets in instants the painless brain-implant, a wedding, kisses and the promise the people will at arrival read the book of revelation written by the Creator. Starfleet orders the Enterpise to leave; when McCoy contacts them about the book, the instrument smites him in pain: Kirk and Spock beam back down...