The left-handed booksellers of London / Garth Nix.

Eighteen-year-old art student Susan Arkshaw arrives in London in search of her father. But before she can question crime boss Frank Thringley he's turned to dust by the prick of a silver hatpin in the hands of the outrageously attractive Merlin. Merlin is one of the youngest members of a secret society of booksellers with magical powers who police the mythic Old World wherever it impinges on the New World -- in addition to running several bookshops, of course! Merlin also has a quest of his own: to find the Old World entity who arranged the murder of his mother. Their investigations attract attention from enemies of the Old and New Worlds. Soon they become involved in an even more urgent task to recover the grail that is the source of the left-handed booksellers' power, before it is used to destroy the booksellers and rouse the hordes of the mythic past. As the search for the grail becomes strangely intertwined with both their quests, they start to wonder... Is Susan's long-lost father a bookseller, or something altogether more mysterious?