Nine year old, Eliza and her dog, Sister have always had a special bond. As far back as she can remember, her big, black dog has been with her and she never questioned where she came from. Eliza lives a quiet, country life with her grandmother and grandfather in Oklahoma. However, the peacefulness of her life and her innocence becomes disturbed when Sister is attacked by other dogs. Eliza holds her dying dog in her arms, feeling the life escape her body, when she is bewildered to see her Sister dog has transformed into a young girl. Eliza's grandmother is left to tell the tale of Sister dog and of the mother she never knew.