A teenager raised alone with extraordinary powers cannot cope with human society, and the Enterprise pays for it.
The Enterprise picks up Charlie Evans, a teenager who survived alone for years after a crash. Charlie is awkward, desperate for affection and secretly able to alter reality with his mind. When he is rebuffed, his tantrums grow deadly.
The episode is a sympathetic tragedy rather than a simple villain story, built around Kirk's attempt to guide a young person who has never learned limits. It gives Spock a moment with his Vulcan harp and Uhura a song, and it is often cited for its themes of loneliness and power.