Chimes at midnight - Seanan McGuire

Things are starting to look up for October "Toby" Daye. She's training her squire, doing her job, and has finally allowed herself to grow closer to the local King of Cats. It seems like her life may finally be settling down...at least until dead changelings start appearing in the alleys of San Francisco, killed by an overdose of goblin fruit.
Toby's efforts to take the problem to the Queen of the Mists are met with harsh reprisals, leaving her under sentence of exile from her home and everyone she loves. Now Toby must find a way to reverse the Queens decree, get the goblin fruit off the streets-and, oh, yes, save her own life, since more than a few of her problems have once again followed her home. And then there's the question of the Queen herself, who seems increasingly unlikely to have a valid claim to the throne...
To find the answers, October and her friends will have to travel from the legendary Library of Stars into the hidden depths of the Kingdom of the Mists-and they'll have to do it fast, because time is running out. In faerie, some fates are worse than death.
October Daye is about to find out what they are.