The Youth Trap " They stand helpless before an alien who dooms them . . . to infancy ! " Summary . As the " Enterprise " scans the planet , no readings of life can be found . Suddenly an alarm goes off and the ship shudders . It is reported that Number Two Engine is taking a beating and may explode ! Just as quickly as it started , the attack ends . Scott reports to Captain Kirk and Spock that every filament part , even those in storage , was burned out by the attack , a part that the engines require to operate . Spock notes that they must find a deposit of Zutotanium . An Engineering team beam s down to the planet to take samples and look for the metal . On the planet , Burns and Lane , the two engineers , begin their sample taking and discover that the rocks are full of the metal . As Kirk responds , a strange noise occurs , and they Kirk loses contact with them . Minutes later , they hear a response , it sounds like two children playing . Spock , Kirk , and Dr . McCoy beam down to the planet and find two children playing with a rock pile . They children seem to be Burns and Lane . As Kirk begins to radio the " Enterprise " , Spock pushes him down as a beam zaps by . they race toward concealment and Spock points out two aliens across the way , firing the beams from a tripod mounted machine . As they ' re entering the cave , McCoy is hit , and is transformed into a teenager . Kirk calls the " Enterprise " and has them beam up Burns , Lane , and McCoy before he and Spock make their way across the canyon toward the aliens . As they do so , Kirk is struck by the beam , and Spock notes that the aliens are speaking Esperanta . Spock pulls Kirk into cover and they notice that the two aliens are fighting with each other , with one pushing the other off the edge of the cliff . Kirk and Spock drag his battered body into shelter as the other alien fires randomly at them . The alien introduces himself as Laiko from the Galaxy Trann , and tells them that he was on an exploratory mission when they had an engine failure and crash landed . Laiko and another of the crew , Kooba , built a machine , but as they were preparing to use it , Kooba slipped and it fired at a nearby lizard . The lizard was transformed into a young pup . They thought that they could adjust the machine to freeze people ' s ages and were testing it on Burns and Lane , and then McCoy . Kirk noticed that the other alien , Kooba , was taking the machine away , back toward the alien ship . The trio follow him and learn that he intends to use it as a weapon against the rest of the alien crew , installing himself as their leader . As the aliens question his authority , Kooba transforms the ship ' s captain into a baby . As this happens , the ledge that Kirk , Spock , and Laiko watch from cracks and begins to slide down the hillside . As the strange sled arrives at the bottom of the hill , they engage in hand to hand combat with the aliens , but are overwhelmed by the sheer numerical advantage that the aliens hold . Kooba threatens them , but notes that they are more valuable to him alive because he plans to return to his homeworld and take over leadership there . However , the alien ship is disabled , but Kooba plans to assume command of the " Enterprise " , which flies overhead . Spock radios up to the ship and Scotty beams him up , along with Kooba and one of the alien guards , Gorg . Kooba has the entire crew stand before television screens , with the intent of firing the age - ray at them over the airwaves . Kooba triggers the ray , and everyone de - ages almost five years instantly , with the rest of the de - aging effect expected to take a matter of hours . Kooba has Gorg beam him to the surface where he intends to turn Kirk into an infant . Kirk avoids the shot and grabs a tin plate and reflects the next shot at one of the guards . Kooba continues to fire at him , and Kirk reflects the shots , eventually hitting Kooba and transforming him into a babe . Kirk quickly frees Laiko , but with Gorg at the transporter controls , they have no way of returning to the ship above . with some quick work , Kirk disguises himself as Kooba , and he and Laiko transport up , and are able to quickly overpower Gorg . Unfortunately , the entire crew has turned into youths . Laiko adjusts the machine and repeats what Kooba did earlier , and the crew begins to return to their original ages . Kirk and Spock return to the planet with Laiko . They return the aliens to their original ages , with the exception of Kooba , before smashing the machine . An engineering team mines some of the Zutotanium for the engine filaments and makes the required repairs . Once complete , Kirk submits a report to Starfleet Command , and tells Spock that the response questioned whether he and the crew had gone " " a little space happy . " " Memorable quotes . " " Suffering sun spots – Our two engineers . . . they ' ve been reduced to five - year - olds ! " " " " Yes , Captain ! And that teen - ager – it is Dr . McCoy as a youth ! " " " " Where in flying asteroids are they ? " " " " Whaaa ? I - I see it . . . but I don ' t believe it ! Captain Kirk . . . Mr . Spock ! L - look here ! " " " " Hi Daddy Kirk and Uncle Spock ! " " " " Are you going to play rock pile with us ? " " " " Looks like we ' ve got our hands full , Spock ! What is our change of nailing that machine and escaping ? " " " " Nil , Captain . " "