The film revolves around two stories: the impending wedding of Lizzie (Cate Blanchett) and Guy (Richard Roxburgh), and a second story, told in flashbacks, of Guy’s previous relationship with Jenny (Frances O’Connor).
Guy and Lizzie meet when Guy brings a pregnant stray cat to Lizzie’s house, believing she owns it. They begin a whirlwind romance and plan to marry six months after meeting. Guy clashes with Lizzie’s wealthy and domineering family, but gives in to their demands out of love for her.
However, during the wedding and reception, Guy experiences flashbacks to his previous relationship with Jenny, a simpler woman with whom he spent most of his twenties. The flashbacks document their relationship from their first meeting to their eventual breakup. It is revealed that Jenny wanted to get married and have children, but Guy was always reluctant to take that step with her.
At the wedding, Guy receives a letter supposedly from a Vietnamese man he’s been corresponding with, but it turns out to be from Lizzie’s mother. Guy is shocked by the deception, but Lizzie downplays it, saying her mother didn’t mean any harm. Guy goes outside and argues with Lizzie, who tells him that marriage requires compromise. At first, Lizzie walks back alone, but Guy follows her. They both seem happy as they head to their bridal suite, but Guy becomes saddened when Lizzie insists he needs to compromise.
Later, Guy spots Jenny on the street and smiles as their eyes seem to meet, but she disappears into the crowd. The film ends with Guy preparing to take Lizzie and their children on vacation, with a voiceover of Guy telling his pen pal that happiness is only truly appreciated over time, making it impossible for him to know if he’s truly happy or not.