When her parents go away for a month-long business trip, Arlie Metcalfe and her little brother, Michael, get to stay with their fun-loving aunt, Isabel. It seems as if it's going to be a month-long vacation, particularly for Arlie, who's looking forward to the time away from her demanding mother. But only a few days into the trip, Arlie's parents are seriously injured in a car accident, and her mother falls into a coma. On the very same day, a new girl arrives in Arlie's fifth-grade class. Casey has the same short brown hair, the same stubbornness, and the same bossiness as Arlie's mother. Is it possible that she is actually Arlie's mother as an eleven-year-old girl? Can Arlie somehow help her mother by befriending Casey? Or is this a gift from the universe for Arlie: a strange and wonderful way to know her mother before she was her mother?