Kate is diagnosed with leukemia when she is three. Her parents and her older brother, Jesse, are not matches for her, but she needs a bone marrow donor. Desperate, her parents turn to genetic engineering and genetically conceive Anna (real name, Andromeda). When Anna is thirteen, she turns to lawyer Campbell Alexander to sue her parents to the rights to her own body so she doesn't have to give a kidney to Kate. Eventually, after a long and involved story that you can look up on your own it's too complicated to describe, we find out Kate wants to die and asked Anna to do this for her. Anna wins the rights to her own body. Unfortunately, as Anna is being driven to the hospital to see Kate after she wins, she gets into a horrible car accident. She is put on life support, but is barely clinging to life, so her parents are going to pull the plug. They decide, because Anna is going to die, they should take her kidney for Kate. Miraculously, the kidney does wonders for Kate and she goes on to live a long and happy life.
There are bunch of other little stories going on at the same time, but this is the general story.