2007 Waterstone's book prize.
From the Guardian:
The novel, inspired by film noir, fantasy and a fascination with the seamier side of the 19th century, is aimed at children between the ages of nine and 12. It tells the story of a boy, Jonathan Stirling, who discovers a parallel world filled with vampires and werewolves. This alternative reality has a distinctly Victorian air, and is ruled by a descendant of Jack the Ripper. Soon bounty hunters from the other side begin searching for Jonathan, who finds himself driven into their world.
Oooo. Sounds fun. Anyone read it?