The story follows Pritam (Mithun Chakraborty), an elderly bus driver. His three good-for-nothing sons, Madhav (Arshad Warsi) the group leader; Laxman (Kunal Khemu) the poetic idiot; and Lucky (Tushar Kapoor) the innocent mute are always up to trouble, mostly by scamming people.
On the other hand, Geeta (Ratna Pathak) is an elderly woman, whose two sons, Laxman (Shreyas Talpade) the stammerer; and Gopal (Ajay Devgn) the strong but kind leader; own a water sports stall at the beach. Gopal & Laxman's partner Daboo (Kareena Kapoor) on whom Gopal has a crush, but never shows it. Three robbers Puppy (Johny Lever), Dagga (Sanjai Mishra) and Teja (Vrajesh Hirjee) rob the queen's necklace and are on the run from police and end up in Goa. Puppy, the don, who suffers from short-term memory, hides the necklace in Pritam's house. Soon enough, Pritam's sons open a water sports shack opposite Geeta's sons' stall, and a rivalry begins.
Filled with mayhem, both the groups try to take down each other's business but fail hilariously. In response to this, Pritam goes to meet Geeta, (although he doesn't know that they are Geeta's sons) to sort this rivalry out and it turns out that Pritam & Geeta were college-lovers. Daboo overhears their love story, and decides to get the two married, without their sons' permissions. After the marriage, the two families start living in one house, filled with non-stop laughs & mayhem. It is also revealed to the five sons that they are not Pritam & Geeta's sons but orphans after overheard by Lucky. Although they vow not to tell them that they know that they are orphans and to hide that, they become friendly like brothers. They also open a big shop of toys aided by Vasooli Bhai (who is another not-so-don don) and Puppy for money.
Puppy eventually remembers where he hid the necklace, and turns himself in along with his goons Dagga and Teja. After the long squabble, chase and mayhem, Gopal and Daboo managed to trick Puppy to take out information of hidden necklace and thus Pritam finds it and gets Puppy and his goons arrested.
This film ends with Pritam and Geeta going out for honeymoon and Gopal, Madhav, Lucky and the two Laxmans end up brawling after an argument.