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 somehow fight the leukaemia that she has plagued her since childhood. Anna was conceived as a bone marrow match for Kate, a life and a role that she has never questioned till now. Like most teenagers, Anna is beginning to ask herself who she truly is. But unlike most teenagers, she has always been defined in terms of her sister - and so Anna makes a decision that for most wold be unthinkable, a decision that will tear her family apart and perhaps have fatal consequences for the sister she loves.