Trying to remember the name of a book...

Hey Guys, hopefully someone can help me out -

I'm trying to remember the name of a book I read probably about ten years ago. I'd say it's geared towards the 6-9 grade age.

It's about a kid who was kidnapped awhile ago, and is now living in the basement of the kidnapper's home, living a "fake" life and afraid to tell his teachers, etc. He breaks out of the house and then says he's part of a family that he isn't really a part of, but he looks enough like the kid that they accept him as their long lost child. Eventually, people suggest that he isn't really the kid and they're investigating it and what not. He's about to confess that he's not really the kid when it ends up (SPOILER ALERT, haha) that he actually was the kid, but had just forgotten because of all the trauma of being kidnapped/beaten etc.

This might not make a lot of sense, but is it ringing any bells?