The Book of Lorath is the next book in the Horadric Vault series and Amazon has a taster. There are five images of pages from the book available to view as seen below.
Book of Lorath Images
The Book of Lorath should be released on 6 June along with the game. There is also the Horadric Vault Collection which includes all the books in the series, the Book of Cain, Book of Tyrael, Book of Adria, and the new Book of Lorath.
Thanks Doomscream.