The Invisible Library by Genevieve Cogman
The Invisible Library is a book lover's dream tale. What could be better than living and working in a library that collects works of literature from alternate realities?
Irene is a professional spy for the Library, sent to retrieve a dangerous book from an alternative, chaos-infested London. To add to her problems, she has to take along her new assistant Kai, an inexperienced rookie with a taste for taking risks.
There is plenty of action and adventure from the very first page. By the end of the book you sense there is more to Irene's past than she even knows herself.