The Private Memoirs and Confessions of a Justified Sinner - James Hogg

I remember trying to read this more than once when I was younger on the basis of its reputation as a Gothic classic, only to come to a halt thanks to the opaque prose style. Even now, I wouldn't suggest that the writing is easy for the modern reader - it is definitely pre-Austen stylistically if not chronologically. However, it does get easier and the rewards are for ploughing on are great.

It is a satire of religious fundamentalism with the trappings of a classic horror story. The central character is convinced that he is destined for heaven no matter what, so he has a mandate to commit any atrocity in the name of God. His diary (presented after a lengthy "Editor's note") reveals the influence both of his hypocritical parents and the mysterious Gil-Martin, who we take to be Satan, a magnificently creepy creation.

It's both funny and scary, and the relevance to the world today is the most horrific thing of all.