The Long-Lost Brother (Sweet Valley High Book 79)

Looks can be deceiving ...
It's no secret that pretty, popular Sara Eastborne has a twin brother named Tim. Sara had told her friends at Sweet Valley High that Tim chose to live with their father on the East Coast when their parents were divorced. But she didn't tell them that Tim was in reform school!
Now Tim's out of reform school and ready to start a new life in Sweet Valley with Sara and their mother. Sara desperately wants Tim to keep his criminal past a secret. When Tim becomes friends with Elizabeth Wakefield and starts dating Sara's best friend, Amanda Hayes, Sara is afraid that the truth will come out and her social life at Sweet Valley High will be ruined.
Tim has betrayed her before, and she isn't going to let him do it again, no matter what.