This mystery/historical novel which takes place in Scotland in 1869 reverts to the popular style of many books written in that period -- it attempts to convince the reader that it is a true story. It purports to be the found written confession of a young man accused of a brutal triple murder. Also included are transcripts from his trial and newspaper accounts. The author, Graeme Macrae Burnet, adds more verisimilitude by giving the protagonist the last name of Macrae, saying that he is an ancestor.
The question is not who committed the murder, as young Macrae readily admits his guilt, but why. As it turns out, Macrae is not the most reliable of narrators. His account of events leading up to the crime and of the crime itself do not always agree with the evidence given at the trial.
I am surprised that this novel was a short-listed finalist for England's 2016 Booker Prize. While it is cleverly written, it seems slight to me.