Absence

Nothing is simple in fifteen-year-old Casey's life. She has two families and two houses and two rooms of her own. Sometimes this makes her feel lucky, but other times she feels practically homeless. She also has a brother with Asperger's. He's interesting to have around, and she loves him very much, but he's also complicated. And speaking of complicated, Casey discovers she's a time traveler. She'll be doing her Algebra homework, or on her way to work at the restaurant, when suddenly she's in some other time and place, in some other body, and she's supposed to do something.
Help somebody. Fix some problem. But how?