There are 6 books that make up that F. Paul Wilson's series of books called The Adversary Cycle. The first three are The Keep, The Tomb, and The Touch can be read in any order. The last three have to read in order, which are Reborn, Reprisal, and Nightworld. All of these novels tie in with Wilson's other main opus of the books, The Repairman Jack series. Jack is the hero of these tales and a force called The Adversary is his foe. These six books are its tale. So you get to see the flip side to the hero's tale.
If you read any of my posts before, then you may already know that I am a huge fan of F. Paul Wilson. I'm on the last couple of books in the Jack series and have finished the first four in this series. I am in awe of how so many of Wilson's story intertwine with his main Jack opus. I dont know if it's intentional or not, but it's very interesting.
Cant wait to finish both of these series and see how it all turns out.