I put the review of all four installment into one post - I read all four in one go, so it even seemed to me like one big story.
And what a great one!
I love the world building, it is done very well, and it has a more original take on the old demons and paranormal cops trope than most books I read.
It has two great main characters: Caleb, the vegetarian hippietwink (possessed by Grey) and John, the paranormal cop and exorcist. An unusual couple with many differences, but also a lot of feeling between them.
But most fascinating for me was how Grey was inserted in the story - I would have liked to see more of him, but maybe this will be the case in the next installment (February 2014 - god, that seems awfully loooong....).
All installments also have a mystery/crime/demon hunt/action plot - they were all good, all a bit creepy and I enjoyed them very much.
If the next one has more Grey in it, it could become a favourite :-)