Conceived by means of in vitro fertilization, Anna Fitzgerald (Abigail Breslin) was brought into the world to be a genetic match for her older sister, Kate (Sofia Vassilieva), who suffers from acute promyelocytic leukemia.

Because of her sister's dependency on her, Anna is unable to live the life she wants; in and out of the hospital constantly, she cannot take part in extracurricular activities such as cheerleading or soccer. When Kate turns 13 she goes into renal failure. Knowing that she will have to donate one of her kidneys to her sister, Anna sues her parents for medical emancipation and the rights to her own body. Attorney Campbell Alexander (Alec Baldwin) agrees to work for Anna pro bono. The film is interlaced with flashbacks that detail the strong relationship between Kate and Anna, as well as how Kate's illness has affected her siblings' lives. Before the result of the case is known, it is revealed that Kate had asked Anna to file for medical emancipation. Believing that she would not survive the surgery, Kate wants to die. Anna wins the case, and due to her sister's wishes does not donate her kidney. Kate later dies at the hospital. The family moves on with their lives, being changed by Kate's death, but every year on Kate's birthday they go to Montana, which was her favorite place in the world.