The story begins with Bethany being mysteriously abandoned with an aunt that she has never known she had. And it gets weirder from there as strangers keep calling her "Elizabeth" and she is stalked by a mysterious man. Eventually, all is revealed, but not before a number of twists and turns.
Haddix writes pretty good suspense, although this story (set in the future) borders heavily into sci-fi. In fact, it's an odd mix of teen angst, child/parent conflict, and a bit of mystery. Makes for good entertainment.