The Rose of Fire is 'book' #2.5 in The Cemetery of Forgotten Books series.
A lovely short story by Zafón that was written to be a teaser for The prisoner of heaven but as with all the stories in the series, it doesn't really matter where you read it. It's set in Spain during the Inquisition and tells the origin of the cemetery of forgotten books. My only complaint is that it's so short! How long do we have to wait till the fourth and final book? I would really recommend this story to all who enjoyed the books.
You can download the ebook free on ebook retailers' websites.