The Left-Handed Booksellers of London
by 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 he's just been turned to dust by the outrageously attractive Merlin. Merlin is a young left-handed bookseller (one of the fighting ones) who, with the right-handed booksellers (the intellectual ones), 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. Susan's search begins with a list of possibly misremembered or misspelt surnames, a reading room ticket, and an engraved silver cigarette case. Merlin has a quest of his own, to find the Old World entity who used ordinary criminals to kill his mother. As he and his sister, the right-handed bookseller Vivien, tread in the path of a botched or covered-up police investigation from years past, they find their quest strangely overlaps with Susan's..."