Sara and Brian Fitzgerald's life with their young son and their two-year-old daughter, Kate, is forever altered when they learn that Kate has Leukemia. The parents' only hope is to conceive another child, specifically intended to save Kate's life. For some, such genetic engineering would raise both moral and ethical questions; for the Fitzgeralds, Sara (Cameron Diaz) in particular, there is no choice but to do whatever it takes to keep Kate alive. And what it takes is Anna.