The thirty and something years old bachelor partners and best friends divorce mediators John Beckwith(Owen Wilson) and Jeremy Grey(Vince Vaughn) have a hobby of crashing weddings following predetermined rules to have one night stand with different women. When they decide to crash the most important wedding of Washington pretending they are brothers, in a party promoted by the Secretary of Treasury William Cleary(Christopher Walken), John breaks their rules and has a crush on Claire Cleary(Rachel McAdams) and Jeremy scores the sex-addicted Gloria Cleary(Isla Fisher), both daughters of William. Gloria invites Jeremy to spend the weekend at the Cleary family estate, and John sees the chance to be close to Claire, in spite of her engagement with the arrogant Zachary "Sack" Lodge(Bradley Cooper). Along the weekend with the dysfunctional Cleary family, John and Jeremy will fall in love for the sisters, but their real identities jeopardize the relationship.
