Stepmom is an American comedy-drama film. Jackie (Susan Sarandon) and Luke (Ed Harris) are a divorced couple struggling to keep their children, Anna (Jena Malone) and Ben (Liam Aiken), 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 around 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 against Luke (as can be seen in a confrontation about Isabel). After a long string of arguments and hurt feelings between Isabel, Jackie and Anna, Luke proposes to Isabel, making her Anna and Ben's official stepmom. This causes even more friction.
However, Jackie is diagnosed with cancer, 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.
Both 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. Yet they manage to call a shaky truce, as both Jackie and Isabel come to terms with the fact that the latter will soon step into the role of surrogate mother.
The two women finally bond with each other when Isabel reveals her admiration of Jackie's maternal instincts, while Jackie in turn compliments 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.
The movie ends with Isabel taking a family picture of Luke and Jackie with their children. Jackie invites Isabel to join them in the portrait, which she does, and as the closing credits begin, both women are shown in a photo side by side, finally at peace with one another and future events (Jackie's death and Isabel and Luke's marriage).