I have always wanted to make one of these secret books!
Firstly find an aptly named book... this one is called "The face of innocence" - perfect!
N.B, if you feel bad chopping up books, find one that has already been ruined, waterlogged, scribed on etc.
Next using a strong PVA glue, glue the edges of the book pages.
Leave a few of the beginning pages out of this gluing... Now leaving the book OPEN, dry it overnight under a pile of heavy books.
When it is dry, mark out where you a going to cut it.
I kinda followed the books' text.
Then begin to cut using a sharp craft knife!
Cut and cut and cut until you reach the bottom...
Now glue the inside pages
Then CLOSE the book and dry overnight
Then cut a piece of velvet to size and hot glue it in!
Then put in all your precious things...
And hide away in the bookcase!