The plot of the film is actually inspired from the Marathi film "Dam Dam Diga Diga" which released in 2008. The film opens with two cousins – Heena (Asin Thottumkal) and Bobby (Jacqueline Fernandez), the two daughters of the Kapoor family who hate each other very much – start quarrelling over something relating to their duties of Animals' Law Authority. Their fathers, Chintu (Rishi Kapoor) and Dabboo (Randhir Kapoor), are step-brothers who hate each other to the very core. Even their wives hate each other. Chintu wants the richest son-in law for his daughter, Heena, while Dabboo too wants the same for his daughter, Bobby. Aakhri Pasta (Chunky Pandey), a marriage counsellor, is ordered by both Chintu and Dabboo to find the best son-in-law. Aakhri Pasta brings Mr. Babani (Virendra Saxena) to discuss Babani's son Jai.
When Chintu misinterprets one of Aakhri's comments, he verbally abuses Babani while shouting. Babani suffers from a condition that affects his heart when he hears loud noises. Due to Chintu's shouting, Babani suffers a heart attack, landing him in a hospital. Babani's son Jai (Shreyas Talpade) comes to know about this and gets angry, then vows revenge, telling his friend Jolly/Jwala (Ritesh Deshmukh), who is the son of billionaire J.D. (Mithun Chakraborty), to go to Chintu, agree to marry his daughter and then break off the wedding at the last minute. Jolly is busy trying to introduce his girlfriend to his own father and does not want to get involved. He suggests Max (John Abraham), their former college mate and a thief, to do the job. Jay goes with Max as his driver, but somehow, they end in the wrong house and go to Dabboo's house.
Jay and Max later find out their mistake. Jai, still wanting revenge, doesn't know what to do and Jolly suggests another former sleazy college mate, Sunny (Akshay Kumar). Jolly goes with Sunny as his bodyguard because Max and Sunny are sworn enemies and as Dabboo's house and Chintu's house are right next to each other, their plan may get destroyed. Sunny and Jolly encounter a crocodile and Max and Jay encounter a snake. They manage to survive the attack.
While Heena and Bobby are on a cruise, they accidentally end up on an island. Max and Sunny become friends again, While Heena and Bobby become friends also. They find a resort and go home. Dabboo gets Jolly (Max) engaged to Bobby and Chintu gets Jolly (Sunny) engaged to Heena. The day of the engagement, Chintu blindfolds Jolly, Sunny, Jai and Heena and takes them to J.D.'s house. After seeing the real Jolly holding Sunny's garland, J.D. Believes that Jolly got engaged to Heena. Luckily, Sunny convinces him. Jolly calls them at midnight and reveals his father's secret of being Jagga Daaku. He also reveals that his real name is Jwala. After Sunny fools Chintu, Chintu calls Dabboo in excitement and tells him that his daughter, Heena, is getting married to Jolly, the son of J.D. Confused, and believing Max to be Jolly, Dabboo takes Max and Bobby to J.D.'s mansion. Sunny handles the situation well by fooling J.D. By taking the name of his religion and tells him that Max is Jolly's friend and Bobby is Max's fiance (though actually it is true) and Max's father is against his and Bobby's marriage. J.D. Then welcomes Bobby, Max and her family to his house and tells them to stay there up to Bobby and Max's marriage.
Batuk Patel (Boman Irani) arrives with his daughter Parul (Shazahn Padamsee) to make things worse. Jay and Jwala come to receive them from the airport. But when they see Parul, Jay and Jwala lie that Jay is Jolly. Parul becomes happy hearing this as they secretly love each other. Jelo (Zarine Khan) gives Jwala the ultimatum — take me to your house or forget me. To help Jwala, Sunny lies to J.D., saying that Jelo is his fiance, and J.D. Again agrees to let her live there as Sunny takes the name of his religion. Sunny and Max lie to their respective father-in-laws that the other guy is the son of J.D. and a maid-servant in the mansion. This creates a lot of confusion.
When Sunny's father as well as Max's 'Guru' tells them never to break anyone's heart, Sunny and Max tell the truth to Heena and Bobby. Enraged, Bobby and Heena slap Max and Sunny respectively, and tell them that they never want to see their faces again. But thinking that instead of telling the truth, Sunny and Max could have done more wrong with them, the two sisters pardon the two boys on the very next day. There Jay and Jolly also let off their plan of revenge on Kapoors on Jay's father's advice. Then Henna proposes Sunny in Sunny's style and Bobby proposes Max in Max's style.
On the day of the four couples' marriage, J.D. and the other brides' fathers learn the truth about the grooms and that they have been lying all this time. Finally, Bobby and Heena convince their fathers to forget their enmity and live together as blood brothers. Chintu and Dabboo join hands and so do their wives. But J.D. was not convinced by them telling the truth, so he turns back into Jagga Daku and starts frightening the families with his gun. He tries to shoot Sunny with his gun as Sunny runs towards J.D. to save him from the falling chandelier and then he understands what was happening. In the end, all the grooms get married to their respective girlfriends.