《海扁王》故事讲述了戴夫·莱泽斯基（Dave Lizewski）一个在美国破落郊区长大的孩子，他不是赌博者、运动员或者坏少年，只是一个平常的孩子。当他没有与他的好友托德和马蒂去当地的漫画店闲逛之时，总会幻想着他学校的老师还有班上的漂亮女孩凯蒂·狄克斯莫（Katie Deauxma）。对于戴夫来说，唯一一件不寻常的事情则是大约一年前他的母亲去世了。但不知何故，青春期的躁动以及遭遇恶棍频繁痛揍所激怒的情绪，使得戴夫决定成为一名超级英雄，自诩名称“海扁王”（Kick-Ass）。戴夫第一次超级英雄行动不幸遭遇了穿刺和轿车碾压的重伤。当他恢复身体后，意识到自己不能轻易地胜任超级英雄。可是，他后来的一次成功地阻止行凶抢劫让美国媒体和大众认识了这个除暴安良的小超级英雄，谁料大毒枭弗兰克·阿米克（Frank D’Amico）把他视为眼中钉。接着戴夫跟随城内义务警员打击犯罪的线索，协同结实的一位志同道合者“红旋风”（Red Mist），开始了他们的超级英雄之路。
A twisted, funny, high-octane adventure, director Matthew Vaughn brings Kick-Ass to the big screen. Kick-Ass tells the story of average teenager Dave Lizewski (Aaron Johnson), a comic-book fanboy who decides to take his obsession as inspiration to become a real-life superhero. As any good superhero would, he chooses a new name, Kick-Ass, assembles a suit and mask to wear, and gets to work fighting crime. There’s only one problem standing in his way: Kick-Ass has absolutely no superpowers.
His life is forever changed as he inspires a subculture of copy cats, meets up with a pair of crazed vigilantes, including an 11-year-old sword-wielding dynamo, Hit Girl (Chloë Grace Moretz) and her father, Big Daddy (Nicolas Cage) and forges a friendship with another fledgling superhero, Red Mist (Christopher Mintz-Plasse). But thanks to the scheming of a local mob boss Frank D’Amico (Mark Strong), that new alliance will be put to the test.
