Overview
On May 1, 1993, at the wedding of Angus and Laura in Somerset, a group gathers, consisting of the always tardy best man Charles; his roommate Scarlett; his posh friend Fiona and her brother Tom; Gareth with his partner Matthew; and Charles's deaf brother David. All are single. In a fluster, Charles forgets the rings and hastily borrows two from attendees, which turn out to be rather mismatched. At the reception, he delivers a suggestive speech and feels drawn to Carrie, an American working in England, and they share the night together. The next morning, as Carrie prepares to return to the U.S., she reflects on how they might have "missed a great opportunity."
Three months later, at the London wedding of Bernard and Lydia – who met at the previous event – Tom takes on the role of best man. Charles is thrilled to see Carrie, who has come back to the U.K., but feels let down to find she's engaged to Hamish, her affluent Scottish fiancé. A young woman named Serena shows interest in David.
During the reception, Charles faces embarrassment from several former girlfriends, including Henrietta, derogatorily nicknamed 'Duckface' by Fiona, whose brother Charles had unintentionally offended at the first wedding. Henrietta accuses Charles of being a "serial monogamist" terrified of commitment. He retreats to an unoccupied hotel suite, where he spots Carrie and Hamish leaving in a taxi. Charles finds himself temporarily stuck in the room when the newlyweds enter for their own intimate moment. Carrie later returns to the reception, and they end up spending another night together.
A month rolls by, and Charles receives an invitation to Carrie’s wedding to Hamish. While looking for a gift along the South Bank, he unexpectedly runs into her. Charles assists Carrie in selecting a wedding dress, during which she shares the details of her 33 sexual partners; when she reveals that Charles was number 32, he awkwardly admits his love for her, but Carrie gently declines his feelings.
Another month passes, and Charles attends Carrie and Hamish's wedding in Perthshire with his friends. The exuberant Gareth encourages the group to seek potential partners; Scarlett meets Chester, a Texas native. Henrietta points out her new boyfriend to Charles. As he watches Carrie and Hamish share a dance, Fiona, noticing Charles's discontent, confides that she remains single because of her feelings for him. Although he is understanding, Charles does not return her affection. During Hamish's speech, Gareth suffers a heart attack and tragically passes away.
At Gareth's funeral, Matthew reads "Funeral Blues" by W. H. Auden. Carrie and Charles share a fleeting moment, leading Charles and Tom to reflect that despite their friends' pride in being single, Gareth and Matthew embodied a committed partnership. They question whether the search for "one true love" is ultimately in vain.
Fast forward ten months, and it’s Charles's wedding day to Henrietta. While arranging seating for guests, Tom unexpectedly encounters his distant cousin Deirdre, and they quickly find themselves enamored. Meanwhile, Scarlett and Chester are delighted to reunite.
Carrie arrives to inform Charles that her marriage to Hamish has ended following challenges they faced. In a backroom at the church, Charles experiences an emotional turmoil. With support from David and Matthew, he resolves to go through with the wedding. When the vicar asks if anyone has a reason to oppose the marriage, David uses sign language to indicate the groom's uncertainties and love for another. In confirming this with an "I do," Charles is met with Henrietta's furious response, leaving him knocked out at the altar and the ceremony abruptly concluded.