Kym (Anne Hathaway) has arrived home from rehab on the day before the wedding of her older sister, Rachel (Rosemarie DeWitt). A junkie since her teens, Kym has been clean for nine months, but her sobriety has not altered her basic personality. Kym is flamboyant and self-centered, but there is a deep core of pain and guilt within her that no amount of bluster and bravado can entirely conceal. Her overprotective father (Bill Irwin) hovers around her like a mother hen. She causes a scene when she learns that Rachel has chosen her best friend, Emma (Anisa George), to be the maid of honor. And she looks forward to the rehearsal dinner so she can be reunited with her superficial mother (Debra Winger).
The wedding might be all about Rachel, but the movie is all about Kym. She is a complicated, volatile individual with obvious bipolar tendencies. Her instability provides a source of dramatic tension, but it never feels forced or artificial.