为了让罹患血癌的凯特能够活下去，父母通过基因技术“制造”了与凯特的基因完美配型的小女儿——安娜。安娜感觉自己只是姐姐凯特的“药罐子”，11年来，凡是在凯特有需要的时候，无论是脐带血还是白血球、肝细胞、骨髓，她都得源源不断的向凯特提供。然而，即使有孤注一掷的妈妈、无可奈何的爸爸，以及身边所有人的爱，凯特的情况还是越来越糟，肾功能的衰竭必须要年仅11岁的安娜捐献出自己的一个肾。这一次，安娜选择了拒绝，并且寻找到律师坎贝尔把母亲告上法庭，她要捍卫自己的身体。然而，法庭上哥哥杰西却吐露了另一番真相……

Anna is not sick, but she might as well be. By age thirteen, she has undergone countless surgeries, transfusions, and shots so that her older sister, Kate, can fight the leukemia that has plagued her since childhood. The product of preimplantation genetic diagnosis, Anna was conceived as a bone marrow match for Kate - a life and a role she has never challenged...until now. Like most teenagers, Anna is beginning to question who she truly is. But unlike most teenagers, she has always been defined in terms of her sister. So, Anna makes a decision that for most would be unthinkable - a decision that will tear her family apart and possibly have fatal consequences for the sister she loves.