Tom, Mia and Oliver are being seriously bullied by a gang of 15 year old girl goths, who call themselves the CIS. Tom's mobile phone is taken, and the girls demand £4 from each child every Monday. This gang is seriously creepy and menacing, and as they go to a different school (and the ringleader has been excluded), and as for various reasons the children don't feel their parents can help, they decide to handle the situation on their own - with disasterous consequences. Oliver, who is rather wimpish but sensible, has doubts about their plans, and the other two begin to suspect a traitor in their midst. The situation is resolved when the police and parents finally get involved, but the real lesson of the book is how badly friendships can be hurt when people mistrust each other. Hard hitting and totally believable, as to be expected from Pete Johnson.