The Shadow in the North - Philip Pullman

Sally Lockhart is twenty-two, and running her own financial consultancy - a thoroughly modern woman in a world of pompous men - but she's about to be thrown headlong into a vicious web of murder, mystery and pure evil. When a client's lost investment appears suspicious, Sally investigates. Soon she is ensnared in a whirl of high-society danger and deceit, which can lead her in only one direction - to the terrifying secret of the Shadow in the North.