 Kirk, Spock, McCoy and a couple of red shirts beam down to the surface of a planet in answer to a fake distress call. There they are overpowered by a small group of human-looking aliens from the Andromeda galaxy, led by Rojan (Warren Stevens). Their galaxy will be uninhabitable within a few thousand years, so they intend to conquer ours, to give themselves a new home. The aliens  spacecraft has been damaged by the energy barrier around the galaxy (first mentioned in the season one s "Where No Man Has Gone Before"), and need the Enterprise to return home, enhancing its engines so that the journey will "only" take 300 years. They take over the Enterprise using their two main weapons - a paralysing beam, and a ray that can reduce a person to a grey block of material - revival only being possible if the block is not damaged. After successfully negotiating the energy barrier, the aliens reduce all the crew into the grey blocks, with the exception of Kirk, Spock, McCoy and Scott, who must somehow overcome the aliens, revive the crew and return home.