经历了上一集中的一番折腾后，舍曼教授（艾迪·墨菲 Eddie Murphy 饰）终于要结婚了，这位幸运的未婚妻不是别人，正是他的同事丹妮丝（珍妮·杰克逊 Janet Jackson 饰）。然而，就在这个节骨眼上，那个隐藏在教授脑中的“第二人格”布迪再度出现。为了期待已久的婚礼不被布迪破坏，教授决定好好对付一下自己的这位“老朋友”。 　　没想到，教授的举动非但没能让布迪消失，甚至让他有了一个独立的身体，脱离了教授掌控的他明目张胆地侵入了教授的生活，并且夺走了教授辛劳多年的研究成果——能够让人短暂返老还童的血清。血清的失窃在教授的家庭里引起了轩然大波，每一个人都渴望着能够享受重回青春的快感。局势是如此的混乱，教授感到梦幻般的婚礼仿佛离自己越来越远。Professor Sherman Klump is getting married. And the Klump family could not be more delighted for him. But Buddy Love, his Mr. Hyde alter-ego from the first film, is back and trying to make it on his own. Buddy keeps resurfacing in untimely outbursts, and threatening the portly professor's marriage plans to colleague Denise Gaines. Utilizing Denise's cutting-edge DNA research, Sherman decides to rid himself of his monstrous nemesis -and his disruptive outbursts-once and for all by extracting Buddy's DNA from his system. But Buddy bursts full-bodied into Sherman's world and lays claim to the professor's astounding invention - a revolutionary youth serum. Desperate to keep it from Buddy, Sherman hides the serum in the Klump family home, thinking it will be safe. Buddy correctly divines where Sherman has placed the serum, but to get it, he has to deal with the entire Klump family first.