Mikoto Misaka, the third most powerful Level 5 psychic in Academy City, has stumbled upon a secret. Along with her best friend Shirai and other members of the student-run law enforcement agency known as Judgement, Misaka has discovered the existence of "Level Upper"—a mysterious tool that grants or enhances psychic abilities. Now Misaka and her friends must figure out who's behind Level Upper and how to defuse it before it claims even more unsuspecting victims!