"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 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. When their parents ask her to donate a kidney, Anna has had...

Cyclists Zoe and Kate are friends and athletic rivals for Olympic gold, while Kate and her husband Jack, also a world-class cyclist, must contend with the recurrence of their young daughter's leukemia.