The Strange Message

Sadie has made some horrible mistakes in her life, and she's trying to make up for them. But no one understands.
One day she suddenly gets a text from someone who's been watching her, but not in the way she thinks. The anonymous messenger is making her do all their dirty work, or else they'll release the darkest secret she'd ever had. Much worse than every one else thinks.
Now Sadie has to figure out how to keep her secret, yet keep her new identity.