By age thirteen, Anna has undergone countless surgeries, transfusions, and injections so that her older sister, Kate, can somehow 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 that she has never challenged until now Anna makes a decision that for most would be unthinkable, a decision that will tear her family apart and have perhaps fatal consequences for the sister she loves