Charles in charge. Teenager Charlie has apparently grown up all by himself, the sole survivor of a transport crash on the planet Thasus when he was just three years old. Rescued by a science vessel, he is beamed aboard the Enterprise so that he can rejoin the human race on Earth Colony 5, but Captain Kirk discovers that the boy is a danger to his ship and crew, possessing the power of transmutation but not having the maturity and experience to use his amazing ability wisely.
As others have pointed out, Charlie X is a lot like the Twilight Zone episode It's a Good Life, in which Billy Mumy abuses his godlike powers to make anything happen, sending those who annoy him 'into the cornfield'. Similarly, when angered, Charlie causes people to vanish, turns them into lizards, makes them become old, or eradicates their facial features. Having not been taught social behaviour or right from wrong, he has become a petulant whiny brat - a boy trying to be an adult - who needs a firm hand to guide him. Kirk does his best to lay down the rules, and risks his life in doing so, but in the end it is the mythical Thasians - those who gave Charlie his powers in the first place - who turn up to make things right, whisking the boy away in the nick of time.
As thoroughly annoying as Charlie is, and as satisfying it is to see him dragged away kicking and screaming by the Thasians at the end, once cannot help but feel a little sorry for the kid: if anyone is to blame for what has happened, it is the Thasians - lousy 'parents' the lot of 'em!
5/10. A fifty minute ship-bound episode, Charlie X feels really drawn out, with pointless padding in the form of a tuneless jam session by Spock and Uhura, and a three dimensional chess game between Kirk and his pointy-eared science officer. Not exactly thrilling stuff!