Looks can be decieving . . .

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 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.

Tim flinched. "Sara, will you just give me a chance? I know I've hurt you in the past, but I'm different now, and-"
"Listen," Sara broke in, her voice a fierce whisper, "I don't want you to tell anybody about the reform school, understand? I told everyone at school that you were living with Dad in Conneticut, that you get good grades, and that you're a member of the track team. And you'd better go along with the story."
Tim's eyes flashed. "You want me to lie?"
"It wouldn't be the first time, would it?" Sara countered.
Tim placed his hands on the table as if to steady himself. He looked carefully at his sister, and then spoke. "Sara, I need to be straight with people about where I've been and what I've done."
"If you don't back up my story, I'll never forgive you!" Sara hissed.
"I have a feeling you'll never forgive me anyway," Tim replied sadly.

What secret is Michael keeping from April? The Girl they Both Loved