Okay, it's not a book, but I just watched this last night, and if you're in the mood for a different sort of horror movie for Halloween - something more psychological than slasher - I think you'll enjoy Session 9.
An asbestos cleaning crew is hired to take on a huge abandoned mental hospital - and get the entire building done in a week, which most of the crew thinks is impossible - but they're promised a huge bonus and agree to take it on. In the meantime, the building starts to have an odd effect on the crew, and tensions rise.
One of the men finds a box marked "Evidence" and inside are recordings of a patient believed to have multiple personalities. The doctor keeps coaxing the personalities to tell him what happened on a Christmas night years ago, and the patient, using different voices, protest and respond in terror. The patient's story starts to unfold as the crewman becomes more and more obsessed with listening to the recordings.
The film was actually shot in the Danvers State Hospital, and in the extras the actors confess being affected by the disturbing setting. Can you blame them?
Take a look, and enjoy.