The Invisible Library by Genevive Cogman

This is a really fun fantasy novel.  Irene is a Librarian for the Library that exists between the alternate worlds of the multiverse.  The invisible Library where she lives is large and Librarians are sent to various alternate worlds to collect books that are considered valuable.  She is sent on her mission with a new trainee named Kai, who seems a bit unusual.  There are fae and dragons, chaos, magic, vampires, werewolves, lots of bad guys and an important book to steal or somehow acquire.  This is the first book in a trilogy.  I enjoyed it and look forward to reading the others.