The left-handed booksellers of London
(Book)

A girl's quest to find her father leads her to an extended family of magical fighting booksellers who police the mythical Old World of England when it intrudes on the modern world. From the bestselling master of teen fantasy, Garth Nix.

In a slightly alternate London in 1983, Susan Arkshaw is looking for her father, a man she has never met. Crime boss Frank Thringley might be able to help her, but Susan doesn't get time to ask Frank any questions. He is turned to dust by the prick of a silver hatpin in the hands of Merlin, a young left-handed bookseller (one of the fighting ones). With the right-handed booksellers (the intellectual ones), they are an extended family of magical beings who police the mythic and legendary Old World when it intrudes on the modern world... in addition to running several bookshops. Merlin and his sister Vivien, are on a quest to find the Old World entity who used ordinary criminals to kill his mother. As they tread in the path of a botched or covered-up police investigation from years past, their quest overlaps with Susan's. -- adapted from jacket