The Peril of Planet Quick Change " An alien form invades the " Enterprise " through Spock ' s mind ! " Summary . Spock has detected a nearby planet that appears to be changing its chemistry every few minutes . The " Enterprise " approaches the planet Metamorpha and it changes again before their eyes . Captain Kirk asks Spock how this is possible and Spock tells him that there are traces of tiantianium , the most precious metal in the galaxy , on the planet . An ounce of this material can propel a starship for a year . The " Enterprise " enters the atmosphere and the crew looks more closely at it with their telescopes . Kirk decides to take a landing party down to the planet and leave Scotty in charge of the vessel . Dr . McCoy , Spock , and a security officer , Crewman Johnson , accompany him . When they beam down , a mountain suddenly rises up beside them , dislodging man - made objects , relics of a long - dead alien civilization . Strange lights rise and attack the party , but retreat from both Kirk and Johnson . Their phaser s do not have any effect , but the lights retreat regardless . They regroup and head toward Spock , swirl around him for a minute , and then vanish as mysteriously as they arrived . The party continues to survey the planet looking for the tiantianium ore with their space - ore detectors . Suddenly , a geyser of water arises while McCoy , Kirk , and Johnson are in a small valley . Spock watches from above on a ledge and tells them to remain calm because they will be saved . He throws a rope to them and pulls all three up at once , surprising them with his strength . He attributes it to adrenalin . He cuts any further discussion by telling them that he has figured a way to extract the ore . However , to do so , they must regulate the planet and return it to normal . Kirk notices that Spock seems to be acting very mechanically , but attributes it to concentrating on the problem at hand . Spock asks for an atomic rocket , four steel girders , and other required materials . They are beamed to the surface , and Spock goes to work , telling Kirk not to disturb him and directs them to a crater to the south . The transports head in that direction with the materials . Meanwhile , it seems that the alien lights encountered earlier are controlling Spock ' s mind . They tell him about how the planet came to be many sun centuries before . A meteorite had pierced the planet in an area where the structure was weak , and impacted the molten mass of its core , changing the internal chemistry . This change vaporized the bodies of the inhabitants of the planet , turning them into light forms . Spock reasons that once all has corrected , the alien life would be returned to their original state . In the crater , Spock wanders into a cave , directed by the aliens , and finds a chemical container that will neutralize the meteorite matter . He puts the chemicals into the rocket and they prepare to fire it at the core . Suddenly the planet begins changing again . The aliens direct Spock to stand and to have the Human s follow his lead . He leads them into a small cave on the crater wall where they will be safe . But the rocket needs to be realigned if " Project Planet Still " is to succeed . They do so and fire the rocket . It burrows deep into the planet , reaching the molten core , losing its chemicals as it does . An eerie mist - lie mixture rises out of the core through the hole created by the rocket . When it reaches the surface , the light forms swirl out of Spock ' s head , and they take humanoid form . The mist continues to form , and a city , Hidenna , arises from the ground . Zarman offers to show them the nearest deposit of the ore which they so desperately seek . As they head toward it , Spock realizes that six aliens entered him , but only five left . One was still inside , Textra , who sought escape , knowledge , and adventure – but Spock was being driven mad . Meanwhile , the landing party has extracted 200 galaxy pounds of the ore . Spock seems to be suffering from the ordeal of having housed the aliens , and Textra will not allow him to reveal the truth . They beam back up to the " Enterprise " , and Spock attempts to tell Kirk by writing down the information . Textra forces him to throw the pen aside , and McCoy insists on taking him to sickbay at once . In sickbay , a thought comes to Spock and he seizes it , leaping up from the bed , and staggering out of sickbay back to the teleportation chamber . He throws on both the materialization and dematerialization beams , and having his body caught in such a neutral zone forces the alien lifeform out of his body and back into its own form . Memorable quotes . " " Spock ! I ' ve had enough of your mumbo jumbo theories ! Look at that – trees sprouting from sand . . . mountains rising ! Nobody or anything can calm this planet down ! I ' m ordering an immediate teleportation back to the " Enterprise " ! " " " " Remain calm , Captain Kirk ! I have my plan nearly completed ! We shall conquer this planet ' s problems ! " " " " Gr - great galloping galaxies – look ! " " " " I always knew there was something unstable about you Vulcan s ! " " " " Dr . McCoy , it seems to me you Earth men can achieve instability even without a machine ! " "