Presenting itself as a dispassionate account of long-ago events, the Editor’s Narrative provides an extensive – if not entirely trustworthy - introduction to the memoirs proper. The tale begins in Dalcastle where the laird, having frittered away his fortune, enters into a marriage of convenience with a wealthy heiress. With little love lost between them, the couple soon separate but not before two sons are born. The hearty, boisterous, outdoorsy George in every way takes after the laird. Robert, his polar opposite, bears more resemblance to Reverend Wringhim, the sanctimonious zealot to whom his mother flees and who, it is hinted, is his real father.

As the brothers mature, an ever-deepening antipathy builds up between them. Robert begins to pursue his brother, “attending him as constantly as his shadow” (p. 46). With uncanny foresight, he seems to know George’s every move in advance and wherever George is, there too is Robert, tormenting him with his devilish presence. The tension escalates into a series of riotous brawls and legal wranglings as the fraternal dispute becomes caught up with the political and religious hostilities of post-Reformation, pre-unification Scotland.

This comes to a head when George is murdered. At first the perpetrator appears to be one of George’s drinking buddies, for the two were witnessed quarrelling shortly before the event. However, it becomes clear from the account of the prostitute and sole witness Arabella Calvert that something much more sinister has taken place. Her tale, one of underhand play and ominous doppelgangers, ultimately points the finger at Robert. However, when the law belatedly tries to catch up with him, he seems to have vanished into thin air.

With the commencement of the memoirs themselves, the reader is led from the faux objectivity of the Editor’s account deep into the warped and terrifying underworld of Robert’s psyche. He essentially retells the tale we have just read but so alarmingly different is his experience of events that it’s almost unrecognisable as such.

Robert’s confessions reveal a mind dominated by a disturbing figure named Gil-Martin, whom he encounters just when he believes his soul to be finally and irredeemably saved. Gil-Martin, who has the power to read minds and to reconfigure his appearance at will, appears at first in the semblance of Robert himself. Playing upon his victim’s solipsism and religious intolerance, he convinces him that he is the scourge of God, a mighty power destined to cleanse the world of unbelievers. He twists the Calvinist doctrines of Robert’s already fanatical belief system in order to goad the ‘justified sinner’ into committing a series of murders – including that of his brother - assuring him that, as he is amongst God’s elect, he cannot be damned.

Echoing his stalking of George in the first part of the novel, Robert finds himself unable to shake off Gil-Martin, whose menacing presence awaits him at very turn. It becomes increasingly ambiguous as to whether his tormenter is the devil attempting to wrest him away from his state of guaranteed salvation or whether he is the projection of Robert’s own ever more disturbed mind. Robert begins to experience prolonged black-outs during which he apparently commits the vilest of atrocities. Whether he is blocking out his own actions or whether Gil-Martin carries them out in his image is left deliberately unclear.

Unable to flee Gil-Martin, Robert finally kills himself. The ultimate destiny of his soul remains an unanswered question.

We are here returned to the Editor’s narrative, picking up again a century later. He discloses to us a letter by James Hogg published in Blackwood’s Magazine about the unearthing of Robert’s body, which is reported to be in a state of miraculous preservation. Abetted by several real-life figures known to Hogg, the Editor reopens the once-more sealed grave. The body, half-decayed already, is rummaged to pieces: alongside it they find a leather case containing a printed pamphlet. Our Editor sets about wresting the mysteries from the “damp, rotten, and yellow” (p. 240) pages. Their contents, of course, are the memoirs we have just read.