Who was pretending to be a doctor in the Black book of secrets?
There already is. Well there are two more but not about the hunt it is all the same characters mostly though. One of the new books is The Black Book of Buried Secrets and one is Vesper's Rising. I have read all the book except Vesper's Rising and I am now finishing the black book of buried secrets. Hope this helps.
If you are referring to the Presidential Book of Secrets, featured in the Movie "National Treasure: Book of Secrets," then there really isn't a book to be found. The presidents' book of secrets is merely access to confidential, secret, or otherwise off limit documents, which each president gains with the office. This access allows the president to know "secrets" about every program, meeting, or project, dating back to the early presidencies.