Traitor, Paperback

Tom, Mia, and Oliver are the victims of a gang of bullies, who waylay them on the way home from school. It's not at school, so the teachers wouldn't be able to help, and they don't want to tell their parents, so there's only one option: to pay up. At first. But as the pressure builds more and more, a terrible suspicion begins to surface: could one of the three friends be helping the bullies? And if so, just who is...the traitor?