Four years after the events of the first film, Dave Lizewski (Aaron Taylor-Johnson), bored after having retired from fighting crime as Kick-Ass, begins training with Hit-Girl Mindy Macready (Chloë Grace Moretz) to become a proper hero. After the death of his father in the previous film, Chris D’Amico (Christopher Mintz-Plasse) is now in control of his father’s criminal empire and reinvents himself as supervillain The Motherfucker, swearing vengeance on Kick-Ass. Mindy’s guardian, Marcus (Morris Chestnut), discovers she is still fighting crime and makes her promise to give it up. Dave’s girlfriend, Katie Deauxma (Lyndsy Fonseca), has noticed Dave behaving strangely and breaks up with him, believing he is cheating on her with Mindy (she also reveals she has cheated on him). Dave resumes his life as Kick-Ass, joining the superhero team Justice Forever (whom Dave had inspired), led by Colonel Stars and Stripes (Jim Carrey). It includes Battle Guy (Dave’s friend, Marty), Dr. Gravity, Insect Man, Night-Bitch, and the parents of a missing child named Tommy. The team works at soup kitchens and patrols the streets before taking on the larger task of shutting down a brothel. Kick-Ass begins a sexual relationship with Night Bitch. He and Marty try to get their friend Todd involved with heroics, but instead alienate him by calling his chosen identity, Ass Kicker, a copy of Kick-Ass. Mindy, attempting to lead a normal life, tries out for the dance team at school, impressing the audience with her audition. Dave tries to convince Mindy to join Justice Forever, but she refuses, and promptly asks a boy to take her on a date. The date ends up as a cruel prank planned by bullies in her school, leaving Mindy abandoned in the forest to walk home alone. Dave consoles the tearful Mindy and encourages her to beat the bullies at their own game. The next day, Mindy does so with verbal put-downs and a crowd-control shock baton, resulting in her suspension from school. Dave’s father discovers Dave is Kick-Ass after finding his superhero costume. Meanwhile, The Motherfucker assembles a gang of supervillains called the Toxic Mega Cunts and establishes an underground lair, including a tank with a live shark. He finds Colonel Stars and Stripes and has his henchwoman Mother Russia decapitate him before taunting Justice Forever on Twitter. He then tracks down Night-Bitch and attempts to rape her, though he is unable to attain an erection. When police arrive, Mother Russia kills all of the officers, resulting in a police clampdown on both costumed villains and vigilantes. When the police track Dave through his IP address, Dave’s father claims he, not Dave, is Kick-Ass. The Motherfucker, unconvinced the real Kick-Ass has been caught, learns from Todd, who had inadvertently joined The Motherfucker’s group, that the man identified as being Kick-Ass is actually his father. The Motherfucker has Mr. Lizewski beaten to death in jail and sends a photograph to Dave, revealing his true identity as Chris D’Amico. A grief-stricken Dave vows to abandon his Kick-Ass identity, as he had promised his father. At his father’s funeral, The Motherfucker’s gang ambushes and kidnaps Dave. Mindy pursues their van, killing all but one of its occupants, rescuing Dave, and convincing him to confront The Motherfucker. Dave and his superhero friends attack the villains’ lair, where a brawl ensues. Hit-Girl is pitted against Mother Russia, who initially seems to overwhelm the outclassed Hit-Girl. However, Hit-Girl tricks Mother Russia into injecting her with a syringe of adrenaline, which gives her the strength to kill her. Fighting on a rooftop, The Motherfucker nearly falls through a skylight, but Kick-Ass grabs him. The Motherfucker refuses help and falls, landing in his own shark tank, where he is mauled and left for dead. Justice Forever decides to give up its superhero duties, helping people in their ordinary lives instead. Mindy tells Dave that because she is wanted for murder, she is leaving New York, but that the citizens need Kick-Ass. She kisses him before departing. Dave accepts the responsibility and begins training and upgrading his equipment. In a post-credits scene, Chris who has survived the shark attack, and whose legs and penis were bitten off by the shark, screams for attention.
戴夫·莱佐斯基（亚伦·约翰逊 饰）不再以“海扁王”身份打击犯罪后过上了无聊的生活，开始把“超杀女”敏蒂·麦奎迪（科洛·莫瑞兹 饰）训练成为英雄角色。意外杀死母亲的克里斯·达米柯（克里斯托福·敏兹-普雷斯 饰）被家族的钱控制，将自己重塑为超级恶棍“臭B王”，发誓要报复海扁王。监护人马库斯（莫里斯·钱雷诺 饰）发现敏蒂仍在打击罪犯，要她发誓放弃这种行为。戴夫的女友凯蒂·多玛（琳德茜·冯塞卡 饰）已经注意到戴夫的怪异行为，认为他跟敏蒂（她告诉凯蒂自己曾骗过戴夫）联手欺骗他，于是跟他分手。戴夫回到了“海扁王”的生活中，加入由“星条旗上校”（金·凯瑞 饰）主导的超级英雄团队“正义永存联盟”，其他成员包括“单挑王”（戴维的朋友马蒂）、“重力博士”、“虫人”、“暗夜骚货”和一对失去了孩子汤米的父母。 小队接到关停一家妓院的大任务之前，在粥厂工 作，还负责街道巡逻。“海扁王”开始与“暗夜骚货”发生性关系，还跟马蒂试图让朋友托德加入到英雄团队中，反倒因托德所选的身份“爆屌侠”——“海扁王” 的翻版而疏远他。 、 敏蒂尝试过上正常的生活，离开了学校的舞蹈队，在试镜时用煽情打动观众。戴夫想说服敏蒂加入“正义永存联盟”，但被她拒绝了，说要跟男朋友约会。但约会最 终因恶霸同学所计划的残酷恶作剧而泡汤，敏蒂被扔在荒郊野林里，要独自步行回家。戴夫安慰哭泣的敏蒂，鼓励她用团队的招数击败恶霸。第二天，敏蒂按照计划 对恶霸恶言相向，还用电击枪教训了他，最终被学校休学。 戴夫的父亲发现了戴夫的“海扁王”服装，意识到儿子的身份。同时，“臭B王”组建了一支超级恶霸帮派“蛇蝎婊子团”，还在地下基地中弄了一个养着活鲨鱼的水箱。他发现“星条旗上校”被追随者“臭俄后”在Twitter斩首，嘲讽了正义永存联盟。后来，他跟踪“午夜骚货”企图强奸，但却无法勃起。当警察到达时，“臭俄后”秒杀所有警察，让两个打扮过的恶棍和义务警员被警察逮捕。警察透过IP地址追踪到戴维，戴维的父亲为了包庇儿子，谎称自己是“海扁王”。 “臭B王”对真正的“海扁王”被捕很不服气，从无意中加入到“臭B王”团队的托德身上得知，被认定为“海扁王”的其实是戴夫的老爸。“臭B王”在监 狱里把莱佐斯基先生打死，还将他的死状拍照，发给戴夫，暴露出他的真实身份克里斯·达米科。悲痛欲绝的戴夫发誓要放弃“海扁王”的身份，这是他答应过父亲 的。父亲的葬礼上，“臭B王”的帮派伏击并绑架了戴夫。敏蒂开着面具车追了上去，打死了所有跟班，救出戴夫，让戴夫跟“臭B王”较量。 戴夫和他的超级英雄伙伴了扫荡了恶棍的老巢，冲突随之而来。“超杀女”跟“臭俄后”面对面，但最初被后者压倒。然而，“超杀女”糊弄了“臭俄后”， 给她打了肾上腺素，顿时力量慢慢。在屋顶的战斗中，“臭B王”几乎从天窗坠地，但“海扁王”拉住他。“臭B王”拒绝帮助，掉进了自己的鲨鱼池中被咬伤。 “正义永存联盟”决定发起超级英雄的职责，改用平常人的身份帮助人们。敏蒂告诉戴夫，自己是被通缉的杀人犯，需要离开纽约去外地避风头，但市民们需要“海扁王”。敏蒂离去前亲了海扁王。戴夫接受了这份指责，开始加强训练并升级装备。 在片尾彩蛋中，克里斯在鲨鱼的袭击中幸存下来，但因腿部和阴茎被鲨鱼咬伤而大声尖叫。