John Beckwith and Jeremy Grey are Washington D.C. divorce mediators who crash weddings to meet and have sex with women. At the end of a season of successful crashes, Jeremy takes John to the wedding of the eldest daughter of the U.S. Secretary of the Treasury, William Cleary. Once inside, the pair set their sights on Cleary's other daughters, Gloria and Claire. Jeremy ends up having sex with Gloria on a nearby beach during the reception. Gloria is possessive and quickly becomes obsessed with Jeremy, and Jeremy urges John to escape the reception with him. Meanwhile, John attempts to court Claire, the maid of honor, but is interrupted by her hotheaded boyfriend, Sack Lodge, who is unfaithful and disrespectful behind her back. When Gloria invites Jeremy and John to an extended weekend party at their family compound in Maryland, John overrules Jeremy to accept and get closer to Claire.
John and Jeremy become acquainted with the Clearys: the Secretary's wife sexually harasses John; Gloria's brother, Todd, tries to seduce Jeremy during the night; Gloria continues to lavish unwanted sexual attention on Jeremy and rapes him after tying his wrists and ankles to a bedframe; and Sack repeatedly injures Jeremy during a game of touch football. At dinner, John spikes Sack's wine with eye-drops to make him sick and get more time to connect with Claire.
John and Claire continue to bond the next day on a sailing trip. The suspicious Sack takes the men on a hunting trip and pranks them, resulting in Jeremy getting shot in the buttocks. While Jeremy recovers, John and Claire go on a bike ride to a secluded beach. Claire finally admits she is not sure how she feels about Sack and ends up kissing John passionately. Meanwhile, Gloria tends to Jeremy's wounds and reveals to him that she is not as inexperienced as she initially let on. Jeremy realizes that he himself has been played and that he may be in love with Gloria.
While John is confessing his attraction to Claire, they are interrupted by Jeremy being chased out of the house. Sack, who had been investigating them, reveals John and Jeremy's real identities to the family. Betrayed, Claire turns on John, and the Secretary tells them to leave.
Over the following months, John attempts to reach Claire, but she refuses to see him. He attempts to sneak into her and Sack's engagement party but is caught and beaten by Sack. Confronting Jeremy about abandoning him, he learns that Jeremy has secretly continued his relationship with Gloria. Betrayed and brokenhearted, John spirals into depression, crashing weddings alone and becoming nihilistic. Meanwhile, as Claire and Sack plan their wedding, Claire's doubts grow. Jeremy proposes to Gloria and tries to ask John to be his best man, but John turns him away.
John visits Jeremy's former wedding crashing mentor, Chazz Reinhold, who convinces John to crash a funeral with him. At the funeral, John reconsiders his belief in love and marriage after seeing the grieving widow. He rushes to Jeremy's wedding and joins the wedding mid-ceremony, to Jeremy's delight. Claire is upset by his appearance, prompting John to express regret for his past behavior and profess his love for her in front of the congregation. Sack interrupts, but Claire finally tells him that she cannot marry him. Sack, whom John refers as Ike Turner, tries to attack John, but Jeremy intervenes and knocks him out, and John and Claire kiss. After the wedding, the two couples drive away from the ceremony together and discuss crashing another wedding together.