From a planet bereft of life for half a million years, the Enterprise hears the voice of Sargon, who is able to control the ship and tells them to transport to specific coordinates which target them to a subterranean chamber. The away party consisted of Kirk, Spock, McCoy and astro-biologist Ann Mulhall; the security guards they planned to take along were prevented from de-materializing. Sargon is one of only three survivors of the planet’s intelligent race – pure energy, matter without form. They tell the away party that they once started life on Earth and many other places. Suddenly Sargon possesses Kirk’s body, saying he requires Spock and Ann Mulhall’s bodies, too, in order to give the only other survivors of his race new life. He promises the bodies will be returned after they build superior mechanical robots as their definitive bodies, then leaves Kirk’s and allows them to beam up and freely make up their minds. McCoy isn’t tempted by curiosity and potential benefits, but Kirk convinces him to re-think his veto. However the human bodies need a metabolic reduction injection; the alien in Spock’s body uses Vulcan mind control to make nurse Christine Chapel give Kirk, Sargon’s host, an injection that would kill Sargon (and also Kirk). Sargon’s wife implores Sargon to leave Kirk’s body before they both die – can Kirk be revived, as his mind is still in Sargon’s mind-receptacle from the planet. The aliens have more surprises in store.