It's very dark, and quite scary in fact.
James Hogg taught himself to read and write, and he wrote this in the early 1800's. It's twisted, and plays games with your head based upon the author using his faith as justification for murder, and a few other atrocities. Scary, pyschological stuff. Way ahead of its time.
...A crotchety older man with a young bride; arranged marriage; rape; religious fervor and zealotry, adultery and more adultery, scandalous liaisons; a serial killer? The devil in the flesh, multiple personality disorder, spirit possession, amnesia? Religious persecution and bigotry, mob mentality. Sightings of Satan; visions, fratricide, matricide, patricide, suicide. Grave robbing, miraculous preservation? Oh yes, and humor. I look at the cover again. No, it isn't Mary Shelley or William Peter Blatty. It's a self-educated man from Scotland. A herder of sheep who was sometimes homeless -- most often penniless -- and who wrote a book that is so multi-layered, so complex, and was so far ahead of its time that it boggles the imagination.
In his book and Calvanistic views, realize that half of the world are doomed to Hell and half are going to heaven....thus the justified part.
This book you will not be able to put down....trust me. You can find it online and read it that way for free.
http://www.pagebypagebooks.com/James_Hogg/The_Private_Memoirs_and_Confessions_of_A_Justified_Sinner/
I prefer to sit and read a good book in real life though, not on the net.