某町不断发生绑架案，被绑架的皆是具有极高运动天赋的女子高中生。一时间各高校人心惶惶，运动社团的女孩更是人人自危。星野（清水由纪 饰）是一个神经大条的女孩，但是阴差阳错，她也遭到了绑架。原来绑架者是一个名为“小丑”的神秘组织，他们妄想征服世界，因此四处网罗身体条件优秀的人进行改造和洗脑，从而创造一支实力超群的军团。当星野再次醒来时，发现自己已经被Joker改造。正在危急时刻，体育老师青山闯入Joker基地，解救了星野，而星野也开始认识到体内所不同寻常的实力。

Released as part of a Neo Action double bill with Tsujimoto Takanori's Hard Revenge, Milly, Kaneko Isao's The Masked Girl follows the giddy action adventures of a high school superheroine called upon to battle supreme evil. On the way home from school one day, high school girl Hoshino Ai (Shimizu Yuki) gets kidnapped by an evil crime organization called Joker, led by devil incarnate Black Maria (Sato Aiko). Ai manages to escape with the help of teacher Aoyama (Kida Tsuyoshi), but realizes she's gained superhero powers after being genetically modified by Joker. She reveals her problems to friend Yumi (Nakamura Shizuka), only to discover that Yumi also been genetically modified and brainwashed to serve Joker. Friends become foes as Ai is forced to fight Yumi, but that's only the beginning of the battle. To take down Black Maria and Joker, Ai must trade in her sailor skirt for superheroine threads, and become The Masked Girl!