In 1984, after a widely publicised debate, the General Assembly of the Church of Scotland agreed to admit as a minister a candidate with a horrific past. James Nelson had fourteen years earlier been sentenced to life imprisonment for the murder of his mother.

The original crime, the Church’s decision and its aftermath are the ingredients of this extraordinary analysis by Stuart Kelly, who is by turns a historical and cultural commentator, a theological and literary sleuth, a dark humourist and a lost but mostly Christian soul seeking his own redemption (though he confesses he would make do with a minor miracle). It is a compelling read, beautifully paced and interspersed with a series of sermons. Chapters open with biblical quotations. It ends surprisingly satisfactorily, reaching no satisfactory answer.

The central issue is the character of Nelson. What caused him to kill his mother, did he ever regret it or repent of it, what led him to seek ordination and what did his past mean to him in his ministry? The evidence suggests that the original crime was an impulsive outburst (in fact he had suffered more from his demanding father than from his mother). He accepted his guilt to the extent that he regarded his crime as ‘explicable though not excusable’. He went on to apply himself diligently to his theological studies both during and after his time in prison. Following his ordination he served as a parish minister. He also married, divorced and remarried. He appeared several times on television as the murderer who had become a minister. Yet these appearances revealed little. Nelson’s inner life remained opaque, which was no doubt one of the reasons he became a cause célèbre. Church and society projected onto him their beliefs about the possibilities of rehabilitation, some insisting his vocation was proof of the efficacy of the Gospel, others wondering if a matricide could ever genuinely acknowledge the depth of his sin. The real Nelson was always likely to disappoint, not being wicked enough for his ordination to be judged a moral outrage, or obviously transformed enough to be an inspiration. There is something simply grey about the man, which no amount of research and reflection can prod into more vivid colours.

It is this frustration that is at the heart of the book. It leads Kelly to reflect on the quirks and quarrels of Scottish church history, on Greek tragedy, on the Bible, on ministers as characters in Scottish literature and on the dark night of the soul for those who have tried and sometimes failed to keep the faith.

The nature of that faith is problematic. Scottish church history is littered with division and subsequent reconciliation. The uncompromising Calvinism that took root in Scotland prized purity and clarity, well-judged rhetoric and speech filled with biblical and literary allusions. The central theme of God’s covenant with his chosen led to a faith of unstinting moral effort and perpetual soul-searching. A suspicion of the apophatic made it hard for believers simply to live in the mystery; everything had to be tortured on the rack of language.

Kelly is a reluctant heir to this tradition, a failed atheist whose faith is at the same time passionate and hesitant. He is not sure whether God is real, at least in this universe, but he is a regular churchgoer and seems haunted by a sense of vocation. In and out of his report of the Nelson affair and its aftermath he weaves his personal story – or at least those parts of his personal story we are invited to see. For the author is also something of an actor: his author photo was taken at the Edinburgh Literary Festival in 2014 and shows a figure seemingly posed in aggressive self-regard, shot in profile, spectacles on nose, hair artfully uncombed, cigarette in fingers. Yet the costume is not all there is; Kelly’s regret and sadness at the breakdown of his marriage come across as genuine, as do the glimmerings of mystical experience and his intuition of evil. As he knows himself to be both Jekyll and Hyde, he seems to conclude that others, and Nelson in particular, are simply unknowable: ‘not truly one, but truly two’.

After Nelson’s death Kelly visited his former parish. He was hoping to get some final judgement on the man through the witness of those who had experienced his ministry. But the evidence was mixed. Nelson appears to have been a competent minister, but not much more than that. His former flock was divided between those who had found him pastorally helpful, mentioning his aptitude for practical matters and his skill at preaching and taking funerals, and those who spoke of a sarcastic, presumptuous streak that had upset some people. Nobody talked about the murder or his first wife, who left him. His original motive and whether or not he ever repented remained unclear. Kelly writes, ‘Every emotional part of me wanted him to be a genuine convert, and every intellectual part of me whispered he was a clever fake’. But as Kelly knows, and elucidates in this disturbingly entertaining book, this unresolved duality is not the plight of matricides alone, it is the mystery of humanity itself, which faith cannot resolve but only endure.