The Enterprise provides transport for 17-year-old Charlie Evans (Robert Walker Jr.), an adolescent who grew up alone on an uninhabited planet after being the sole survivor of a crash 14 years before. Initially unbeknownst to Kirk & Co., Charlie holds powerful abilities that were given to him by an alien race so he could survive his isolation. Charlie now finds himself unable to cope with life among humans, as he careens into social situations where, when he doesn't understand, he feels forced to throw people upon the mercy of his own abilities—including making people "go away," vanishing into apparent oblivion.
The true success in "Charlie X" is in its central character's sympathetic dilemma. Charlie is a boy who wants to be liked and understood, but he doesn't grasp the social norms, and as a result feels threatened whenever he is faced with anything approaching the unpleasant or adversarial. When he experiences a crush on Yeoman Rand, his determination to win her over is poisoned by his ability to harness his anger when his feelings aren't returned.
The episode depends less on plot manipulations than it does on intelligently analyzing one person and the understandable problems surrounding him. Walker Jr. turns in a vivid performance, making Charlie pitiable even when he's at his most sadistic and malevolent. His face-off scenes with Kirk are right on the money. The story's conclusion is a necessary yet unfortunate turn of events.