Plot

A being that controls matter and creates planets wants to play with the Enterprise crew.

When Kirk and Sulu vanish into thin air from the bridge of the Enterprise, Spock sends a landing party to the planet below to locate them. What they find is an 18th century castle and a rather foppish man, Trelane, who seems to know a great deal about the Earth - even if it is the wrong time period. If truth be told, Trelane acts like a spoiled little boy and it's obvious Kirk and the others have become his playthings. They soon realize that if they are to overcome Trelane and free themselves, they must locate and destroy his power source.—garykmcd

As the Enterprise encounters a lifeless planet, suddenly Sulu is zapped off of the bridge. Kirk, reaching toward him in concern, is as well. The ship receives old style western messages from the surface and know that there is life down there.

Spock dispatches a team of Jaeger (Richard Carlyle), McCoy and Desalle (Michael Barrier), wearing masks to defend against the noxious gases (as detected from the ships's sensors). Once below, Jaeger gives the OK to remove masks as the atmosphere is similar to Earth... The team enters a castle and sees Sulu and Kirk, who are frozen. Voila, here is Trelane (William Campbell), an effeminate dandy, dressed in frills and speaking like a woman. Trelane expresses himself in a fancy manner but his desires are for beauty, not relations. The team and the unfrozen Kirk and Sulu are beamed away by Spock on-board ship, who has been able to use the ship's sensors to figure out that Kirk and the other team members are on a specific part of the planet, seemingly able to support life.

But Trelane is not a pushover. He comes aboard the Enterprise & has the power to freeze the whole ship, and he does. Kirk is righteously upset, and beams more of his people down, including Spock who Trelane does not like. Spock says "I object to power without discipline." Trelane learns accidentally that there are women aboard, and transports two down. Uhura and Yeoman Teresa Ross, dressed in red with black leggings, her full blond hair kept above, and very young. Trelane changes her into Cinderella, complete with ball gown, and a strap from the foot of her white pearled dress attached to the wrist to prevent trailing during a dance. As Uhura is forced to play the harpsichord which she enjoys because she didn't know how previously, Trelane dances a minuet with Yeoman Ross. Kirk and Spock reason that Trelane knows all of Earth forms but none of its functions (food and wine are tasteless etc).. They reckon he has a machine that does all this for him.

Now Kirk has time to discover Trelane's power source, his large mirror, and he challenges Trelane to a duel. Trelane is distracted by the dance with Teresa Ross, who is smiling and enjoying dancing. Disturbed by Kirk's feigned jealousy, but seeing another fun opportunity, agrees. They each take a pistol, but Trelane claims the right to shoot first. He nobly fires into the ceiling. Kirk smiles knowingly, but fires at the mirror, Trelane gives a sharp look to Kirk. Clearly, he is displeased. The power is destroyed and all return to the ship. Yeoman Teresa Ross asks if she can change out of her Cinderella clothing. Kirk is embarrassed and blushing and says sheepishly yes.

Trelane is not that impotent. He follows the Enterprise on a collision course with the Planet. Kirk transports himself to Treland, as he sits above in judge's robes and wig. "Did you really think that was ALL of my power, Captain?" In desperation, Kirk challenges him to a royal hunt, with himself as the hunted, which extends the inevitable a few more minutes. Suddenly,Trelane's parents (disembodied voices) arrive to take him away from his toys (his predators) and apologize to Kirk for their son's interference. Kirk is back aboard and relieved. Finally he can relax. No one died, not the Yeoman or Uhura either. He tells Spock "Trelane was a small boy." The Enterprise is safe. Kirk has discovered that power and maturity do not always equate.