Emma Allen and Olivia 'Liv' Lerner are best friends who have planned every detail of their weddings, since first witnessing a wedding 20 years ago at the Plaza Hotel. They both have made it a priority to be married in the same location in June.
The two get engaged at 26, and are expected to be each other's maid of honor. They schedule their weddings with New York's most famous wedding planner, Marion St. Claire, but due to a clerical error they are scheduled to have a wedding on the same day, June 6 (three and a half months later). A week of passive aggressive hostility passes before the two women make it clear that neither will compromise, especially after the headstrong Liv hopes that Emma's passive nature would end their wait of who will surrender their date. Emma's fiancÃ©, Fletcher, begins to show signs of being controlling. The two women declare war after a slight misunderstanding that Liv already set her wedding date, outraging Emma who sets her date as well, which Liv becomes aware of at their shared shower party. The two exchange threats and insults in front of their friends who decide not to take sides.
Both women attempt to sabotage each other's wedding, including Liv changing Emma's dance instructor, Emma secretly sending Liv candy to make her too fat to fit into her dress, Liv making Emma's tan turn bright orange, Emma tampering with Liv's hair dye to turn Liv's hair a shocking blue-white color, Liv registering Emma on Babies-R-Us as pregnant, and Emma showing up to Liv's bachelorette party to out-dance her. Emma and Fletcher get into an argument regarding Emma's maniac behavior of sabotaging Liv's wedding and their friendship. Emma and Fletcher are shown to undergo strains in their relationship because of Emma's new found opinionated and confident trait, a depart from her usual people-pleasing characteristics. Liv has learned to be more sensitive and expressive, which gives her a sense of relief to finally have the luxury of being able to let go and be less controlling.
Both brides-to-be are shown to be in the Plaza very shortly before they are due to be wed, separately. Right before Liv leaves to begin her march to the altar, she encounters Emma's father and receives his blessing; immediately she regrets setting up a wild spring break DVD to play at Emma's wedding. She sends her assistant Kevin to replace the DVD with the right one, filled with childhood memories. Thinking that the DVD is for a prank, he does not do so. Before the brides enter their respective venues, they share a moment of reconciliation as they both smile at each other.
Emma begins her walk down the aisle but stops when the footage of her spring break is shown. She loses her temper and tackles Liv after sprinting to the other section of the Plaza. The two brides wrestle in their dresses on the floor while the people closest to the brides having decided to let the brides resolve the problem. After tussling, Emma and Liv lie on the ground panting, and then make up. Emma stands up and walks over to Fletcher who is upset at Emma's behavior. Emma tells him that she is not the same person he fell in love with ten years ago and that she has now changed, as it has been apparent that she learned to be more assertive. With that, the two tearfully call off their wedding. Liv's wedding resumes with Emma participating and dancing with Nate, Liv's brother and a well known magazine journalist.
The movie picks up a year later when Liv and Emma meet up for drinks, where it's revealed that Emma married Nate. Emma and Liv also reveal to each other that they are pregnant and that their due dates are the same, March 3, and both friends get excited.
Who is Liv's assistant?
Kevin