The Enemy:

When the sickness came, every parent, every policeman, every politician...everyone over 16 years old fell ill. The lucky ones died. The rest begin to decompose, becoming crazed, confused, and hungry for young flesh. Now, every child and teen must fight for survival against the ferocious adults who hunt them in packs, like wild dogs. In the first three books of Charlie Higson’s hit series, desperate groups of children in London struggle to find a safe place to live and a way to survive in this new world where death roams the streets.