Plot

When two weddings are double-booked at the same venue, the father of one bride and the sister of the other bride try to preserve the wedding weekend.

When two weddings are accidentally booked on the same day at the same venue, each bridal party is challenged with preserving their family's special moment. In a hilarious battle of determination, the father of one bride (Will Ferrell) and the sister of the other bride (Reese Witherspoon) chaotically go head-to-head as they stop at nothing to uphold an unforgettable celebration for their loved ones.

Overattentive single father Jim (Will Ferrell) is shocked to hear that his daughter, Jenni (Geraldine Viswanathan), has gotten engaged to her boyfriend Oliver (Stony Blyden). Jim still sees Jenni as a little girl and cannot believe that she has grown up into a woman who can make her own choices and decisions. Jim believes that Jenni is too young to get married and is livid that Oliver did not ask for his permission before proposing to Jenni and had made plans to live together. Jim finally accepts Oliver after a yelling match with Jenni.

Jim calls to book the small inn on Palmetto Island, Georgia, the same place where Jim and Jenni's mother were married before her death from cancer. The owner, Scarlett, accepts his reservation for June 1, but abruptly dies before she can fill out the booking on the inn's calendar. Jenni's friends are Heather (Keyla Monterroso Mejia), Lexi (Zamani Wilder) and Kelly (Ramona Young). Oliver's friends are Josh (Joshue Charles) and Sam (Matt Mercurio).

Meanwhile, television producer Margot (Reese Witherspoon) finds out that her sister Neve (Meredith Hagner) plans to marry her boyfriend Dixon (Jimmy Tatro), an exotic dancer. Neve is upset that their mother does not approve of her choice of life partner. Margot is also estranged from her mother and other siblings and is only close to Neve in her entire family. Margot also volunteers to plan the wedding, also booking Palmetto Island, where she and Neve visited their grandmother as children. Leslie (Jack McBrayer), Palmetto House's new manager, takes their booking for June 1, unaware of the previous booking.

On the weekend of the weddings, both parties arrive and discover the double booking. Jim is able to prove that Scarlett took the booking as there was a pen marking on the calendar book, but no ink as the pen was not working. But officially the booking belongs to Margot as her credit card is the only one on file. Heather was Jenni's wedding planner, and she never came to the Island once to check the arrangements, while Margot had done 3 site visits.

Since the island is too small to accommodate two weddings, Margot initially claims the venue for Neve and Dixon, but they later agree to share the island by alternating between indoor and outdoor events. Margot was moved by the story that Jim is a single dad, who baked a wedding cake for Jenni and that their only other option is a wet and wild water park about 200 miles away. The agreement was to share the sunset with Jenni doing her wedding in the first part of the sunset and Neve going next in the 2nd part of the sunset.

Neve reveals to Margot that she is pregnant but asks her to keep it a secret to avoid upsetting their traditional mother Flora (Celia Weston). Neve & Margot have sister Gwyneth (Leanne Morgan), brother Colton (Rory Scovel) and his wife Rebecca. Pastor Jerry (Wesley Mann) is a family friend. Margot has fired Pastor Luther (Nick Jonas) for the ceremony which offends Jerry.

At the rehearsal dinners, both parties are forced inside by a rainstorm. Jim charms Margot's siblings and mother, frustrating Margot, who has a strained relationship with her family. Flora will constantly put Margot down in front of the family. She is excluded from the family picture and her achievements are undermined in front of the non-achievements of Colton (who has an obscure business helping other businesses in the field of business) or Gwyneth (whose house is being featured in Guns and Gardens magazine). Jim and Jenni perform Islands in the Stream together, disturbing Margot with the sexual undertones of the song.

Afterwards, Margot makes a drunken toast. When Jim attempts to take the microphone from her, she accidentally hits Jenni in the face with it. In the morning, Jim overhears Margot criticizing Jenni's appearance and her closeness with her dad to her family, who defend Jim.

As an act of revenge, Jim intentionally draws out Jenni and Oliver's ceremony so that Neve and Dixon will not be able to marry at sunset, then enlists a boat to drive past the dock where their ceremony is taking place to splash the wedding party. On a second pass, the dock collapses, dropping the family into the water.

Jim and Margot meet up later in the evening, where Margot apologizes to Jim, only for him to guiltily admit to his revenge plans. A furious Margot enlists her siblings to ruin Jenni and Oliver's reception by destroying their wedding cake.

Afterward, the siblings have a heartfelt conversation, where each of them opens up about their life problems. Colton says that banks already do what he does, and he is only sustaining due to his father-in-law who emasculates him. While Gwyneth says that she is bored with her life and the accident at the dock was the most alive she felt in many years. While they are talking, they see someone who appears to be Oliver outside the hotel kissing a bridesmaid. Margot tells Jim, who is dubious.

After finding out from Oliver that he and Jenni are planning to move from Atlanta to Memphis and had been hiding it from Jim, however, he reveals the information but implies that he witnessed the moment himself. A furious Jenni begins kissing other attendees at random, leading Oliver to do the same with a bridesmaid.

Amid the chaos, it is revealed that the person Margot saw was one of Oliver's groomsmen. Jenni angrily leaves Jim and the island behind, while Neve and Dixon complete their interrupted ceremony. At the reception, Margot fights with her mother over her emotional unavailability, revealing her sibling's secrets in the process, while her family criticizes her for being distant from them.

When Margot returns to her room, Jim is waiting with an alligator, which bites her before he throws it out of the hotel window. Dixon (who is a trained medic) treats the injury, and Margot reconciles with her family and with Jim.

When Jim discovers through social media that Jenni and Oliver have annulled their marriage, he gets a ride with Margot back to Atlanta to try to convince her to go through with the marriage. He and Jenni have a heart-to-heart, agreeing not to lie to each other anymore. She and Oliver decide not to get remarried, but still plan to move to Memphis together and remain a couple.

Afterwards, Jenni reveals to Margot that Jim is romantically interested in her. The two make plans to see each other again and share a kiss before Margot returns home. The following Thanksgiving, Margot's family, along with Jim, Jenni, and Oliver, visit her in Los Angeles and take a family photo together. Jim proposes to Margot, who instead suggests that they elope in order to avoid another wedding fiasco.