Roddy Macrae is a murderer. This is something he admits quite freely.

Roddy is the son of "the Black Macrae," a pious, severe man named for his dark complexion. A poor crofter (farmer, in old Scots speak), the Black Macrae was harassed out of his meager living by a bully of a man who was propped up by a corrupt feudal system.

We learn all of this from an extraordinary document: Roddy's written confession, in which he admits to killing three people in order to avenge his father's wrong. Extraordinary because it's 1869, Roddy is a poor 17-year-old from a tiny, destitute town in the Scottish Highlands and yet Roddy can write — well and engagingly.

That's a good thing for us readers, since his account makes up the bulk of this gripping, unnerving novel, a finalist for the 2016 Man Booker prize.

Roddy is unusually gifted. (The master in the nearby school even tries to get the gloomy Black Macrae to let Roddy get an education and break free of the serfdom of their lives. The Black Macrae refuses, of course.)

Roddy paints a detailed and unrelentingly bleak picture of his early life and of his dour father, who beats the admittedly odd and isolated Roddy mercilessly and on a regular basis. The only highlights in life are his mother and his sister. But his mother, "beautiful and gregarious," dies young and takes the family's sliver of joy with her. His father swiftly forces his sister to fill his mother's role (although just what that entails he only hints at). A suffocating despair settles on the family hovel.

Roddy doesn't ask for our sympathies; he exacts them, as he, with little or no emotion, lays bare the facts of his brutal life. But our sympathies only go so far when it becomes clear that there's something not quite right about Roddy — or his well-composed confession. He lets drop just enough hints to give us doubts about his character and his narration.

His description of how, out of mercy, he put a sheep that has broken its leg out of its misery is a little too lurid for comfort. He lets slip an indecorous line or two about his sister. And he recounts his own bizarre reactions to what seem to be everyday occurrences in his feudal village.

His advocate, one Mr. Andrew Sinclair, asked Roddy to write his account, ostensibly to help convince the jury that the grinding poverty and increasing brutality to which Roddy and his family had been subjected drove him mad. Roddy complies, claiming he is doing so not to "absolve myself of the responsibility of the deeds which I have lately committed," but to "repay my advocate's kindness toward me."

The novel — which also includes statements given to police, medical reports and trial transcripts — is so believable that it reads like a historical account, not fiction. The footnoted preface from the author, Graeme Macrae Burnet, claiming he ran across this bloody story while researching the life of his grandfather, serves to argue for the book's authenticity.

But it's not fact, it's fiction — riveting, sometimes even grotesque, fiction. So the book's lackluster conclusion seems all the more disappointing.

In the end, Roddy remains a mystery, his motivations and mental health uncertain. The only thing that's clear is his what he did — his bloody, bloody project.

Connie Nelson is senior editor for lifestyles at the Star Tribune.