Double Identity - Margaret Peterson Haddix

Bethany is a teenage girl that has been spoiled all of her life. Her parents pretty much give her whatever she wants, and she has had an ideal childhood. Then suddenly, her father becomes extremely overprotective, and her mother falls into a deep depression. Suddenly, they get in the car and drive across the country, only to leave Bethany with an aunt that never knew existed, and is just as clueless about the situation as Bethany. Her parents disappear, and tell her that it is too dangerous to contact them. People in her aunt's hometown look at Bethany as though they have seen a ghost. Soon, a strange man comes looking for answers, and Bethany realizes that there might be more danger than she realizes.

This is a very quick read, aimed at older children. I would recommend it to older elementary and junior high students.