You've Got Blackmail by Rachel Wright
My heart is now thumping like the clappers. Panic is rushing through my veins. What in the name of Nora am I going to do? Jaffa Cake junkie Lozzie Cracknell is a girl on the edge. She's been caught borrowing her sister Karen's stuff; her mum's possibly 'doing-the-do' with her worst teacher; and school bully and vanilla blancmange look-alike, Tonia Ravonia, is threatening to head-butt her halfway to hospital. Still, looking on the bright side, at least she and her best mate, Dex, haven't stumbled across a seriously scary blackmail scam, or found themselves on the trail of the blackmailer. Yet.