I picked this book up more or less at random, never having heard of it or Hogg before. Havng read it, I can't believe it doesn't have a higher profile as a classic of British literature, because it is one of the most startlingly original books I have ever read, and was well before its time in terms of structure and themes.
The book consists of two parallel narratives. The first is of an editor, who comes across the strange tale of a murder over 100 years after it occurred. The story is that of two estranged brothers, George Colwan and Robert Wringham. George is the heir to a lairdship, while Robert and his mother are thrown out of the estate because of her religious zeal and the possibility that Robert was fathered by another man (the sinister religious tutor for whom he is named). Burning with hate, Robert stalks George and a series of unpleasant episodes ensue which culminate in George's murder, and the disappearance of Robert and his mother. This is all told as a dry legal matter. The second narrative is Robert's diary, retelling the same events but with a decidedly supernatural twist. It is a brave move by the author to make the least sympethetic character in the book its narrator. Robert's actions are explained because he is morally unconstrained, because he has been told that his place in heaven is assured. As soon as he becomes aware of this, the stranger Gil-martin appears at his side, persuading him to do evil acts in the name of goodness, including the murder of his brother and his eventual flight and suicide.
There is so much to enjoy about this book. It is ostensibly an attack on predestination (the religious view that some people are chosen by God for heaven before they are born, and that nothing that they can do on earth alters this destiny). Gil-martin's identity remains ambiguous: he encourages Robert to use this freedom to commit acts that people who need to curry God's favour cannot, and it is strongly hinted that he is the devil, though Robert never proves this to himself, and Hogg avoids being explicit about his identity. Thus the book anticipates later existentialist literature, by asking how a man with no moral boundaries should behave in the world (much the same dilemma faced by Dostoievsky's Raskolnikov or Camus' Meersault). If Gil-martin is the devil then Robert has chosen poorly, but it is just possible that he is actually an avenging angel, using a newly freed Robert to cleanse the world of evil in a way that one constrained by the need to attain heavenly favour could not do. It is the maintenance of this moral ambiguity that is unexepected in a book written in 1824.
Furthermore, there are elements of both whodunnit and horror. The whodunnit stems from the murder itself, about which we are given no detail until George's adoptive mother turns sleuth, although we always know that Robert is the likely suspect. But the motive isn't explained until the second narrative, which develops the supernatural theme with the introduction of Gil-martin and continues with Robert's flight, followed all the while by demons. This does become genuinely spooky, and the imagery of Robert turning into some ghoulish spider after becoming trapped in some yarn being spun is cinematic in the extreme.
But the real joy in the writing is the ambiguity that Hogg maintains throughout. Initially he sets the story up as being historically true, being the result of legal documents and a found diary. We are then forced to question Robert's perception of events. His diary clearly lies in places (e.g. how George was killed), and the reader is left wondering if we can trust anything he says. Gil-martin takes on different facial features constantly, evidence to Robert of his supernatural powers, but evidence to us, perhaps, that there was no Gil-martin (he is not mentioned in the first narrative) and that all the people he mimicked were real and the devilry came very much from Robert. Was Robert visited by the devil, or was he just trying to hide his own evil, somewhat like Anthony Perkin's character in 'Psycho', who transferred all the blame for his acts by dressing up as his mother when he did them? Unlike that film, this is never resolved in the book, but is a wonderful example of psychological fiction. The ambiguity doesn't stop there though, as we are told that the whole story comes to light through the reminisces of a local shepherd who is shown to be a notorious liar, and his name is...James Hogg. So we have the very Borges-esque theme of the novel as a lie, the retelling of a lie by a liar, but presented as the truth. This is beautifully clever and the novel is brilliantly crafted to retain its plausability.
I suspect that the book is so obscure that very few people will read this review. If you come across it, like I did, by accident, then use it as an opportunity to read one of the most unique books I have ever read. It is superb, and deserves greater attention.