If you are a fan of occult fiction but have never read any of Dennis Wheatley's novels I highly recommend you try one. I discovered his work because of two of my favorite Hammer films - THE DEVIL RIDES OUT (a.k.a. THE DEVIL'S BRIDE) (1968) and THE LOST CONTINENT (1968). Both are adapted from Wheatley books and both are fantastic stories. There have been other screen adaptations and several of them are good but I would point you toward his novels if you can handle their archaic writing style.
Check out this British documentary for a pretty good introduction to the man and his work.