The book that wouldn't burn / Mark Lawrence.

The boy has lived his whole life trapped within a book-choked chamber older than empires and larger than cities. The girl has been plucked from the outskirts of civilization to be trained as a librarian, studying the mysteries of the great library at the heart of her kingdom. They were never supposed to meet. But in the library, they did. Their stories spiral around each other, across worlds and time. This is a tale of truth and lies and hearts, and the blurring of one into another. A journey on which knowledge erodes certainty and on which, though the pen may be mightier than the sword, blood will be spilled and cities burned.