This book was an experience. Early on it just seemed basically all right, I was expecting a 3 or 3.5 rating. As I read my enjoyment started to rise, with multiple revelations taking place in the second half which not only were brilliant to read but made me retrospectively see the first half of the book in a different light.  Friendships and relationships formed which were a joy to read. The final events felt five star worthy and left me wanting to hug the book to myself. 

I honestly don't think I can talk about the plot very much without giving spoilers you might be best avoiding. What I will say is that doors travelled through via the Book do not have to exist in the present day. And certain things might not be quite what you expect. 

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Do be aware that there are some gruesome deaths and terrible things which happen which are unpleasant to read.