Three books I recommend for the fans of horror, the supernatural, and conspiracy are "Adam" by Ted Dekker, "House of Bones" by Graham Masterton, and "The Book of Lies" by Brad Meltzer.
"Adam" is another supernatural based thriller involving the FBI, a serial killer, demons, and the usual Dekker twists. It is dark, creepy, not overly gory, and sustains one's interest till the end. I liked it.
"House of Bones" was an unusual pick because it is a relatively short (236 pages)and while hardcover, almost the size of a paperback, set in almost Large Print, which I liked for late night reading. It takes place in contemporary England, and the main creepy characters are Druids. It was intriguing, and a great short read. I'll be doing some research of Druids and ancient sites of England, inspired by this book.
"The Book of Lies" written by the author of "The Book of Fate" is one of my favorite themes, religious/political conspiracies. The Thule Society (Aryan/Nazis) want the Mark of Cain from the bible story for their own power and glory. It also included "Superman" and his creator as part of the central plot. What fun!