A terminally-ill woman must deal with her ex-husband's new lover, who will be their children's stepmother.
Anna and Ben, the two children of Jackie and Luke, must cope with the fact that their parents divorced and their father is now with successful photographer Isabel. She does her best to treat the kids in a way that makes them still feel at home when they're with their dad, but she also loves her work and doesn't plan to give it up. But full-time mother Jackie finds Isabel's efforts offensively insufficient and can't understand that work can be important to her as well as the kids. The conflict between them is deepened by the sudden diagnosis of cancer, which might be deadly for Jackie. They all have to learn a little in order to grow together.
- Jackie and Luke Harrison (Susan Sarandon and Ed Harris) are a divorced couple that are struggling to help their children Anna (Jena Malone) and Ben (Liam Aiken) be happy with this sudden change of lifestyle.
This is far from easy, as Luke, an attorney, is living with his new girlfriend Isabel (Julia Roberts), a successful fashion photographer several years his junior. Isabel tries very hard to make Anna and Ben feel comfortable and happy with her, but Anna repeatedly rejects her overtures while Ben, who is generally kind to Isabel, adds extra complication with his mischievous nature. Isabel behaves with contempt tempered by caution around Jackie, believing she overcompensates for her divorce by spoiling her children. Conversely, Jackie, a former publisher turned stay-at-home-mom, gives Isabel a cold reception, seeing her as an overly ambitious career woman. She also continues to harbor malice towards Luke (as can be seen in a confrontation about Isabel). After a long string of arguments and hurt feelings involving Isabel, Jackie and Anna, Luke proposes to Isabel, making her Anna and Ben's soon-to-be official stepmom. This causes even more friction.
However, Jackie is diagnosed with lymphoma, which is discovered to be terminal. She experiences a range of negative emotions, angry at the woman who she feels played a role in her broken family, and angry at the fact that after all of the sacrifices she made for her family, she will not even get to see her children grow up. Jackie and Isabel clash repeatedly, largely over Isabel's parenting. This becomes evident when Ben goes missing on Isabel's watch and Jackie claims that she has never lost him, which she later admits to be untrue. However, they manage to establish a shaky truce, as both Jackie and Isabel come to terms with the fact that Isabel will soon step into the role of surrogate mother.
The two women finally bond when Isabel reveals her admiration of Jackie's maternal instincts, while Jackie in turn praises Isabel's hipness as a means to connect with Anna. Isabel finally lets her guard down when she tearfully tells Jackie her biggest fear is that on Anna's wedding day, all Anna will wish for is her mother's presence. Through her own tears, Jackie says her own fear is that Anna will forget her. Jackie explains to Isabel that, while Jackie will always have their past, Isabel will have their future.
The film ends with the family celebrating Christmas. Jackie, bedridden from her illness, is visited in her room by Ben and Anna. Individually, Jackie tells her children after giving them their presents that even though she will die, she will always be with them as long as they remember her. Later that day, Isabel is taking a family picture of Luke and Jackie with their children. Jackie demonstrates her acceptance of Isabel by inviting her to join them in the portrait, stating "let's get [a photo] with the whole family". Isabel does, and as the closing credits begin, both women are shown happily in a photo side by side, finally at peace with one another and future events (Jackie's death and Isabel's marriage to Luke).