Those of us too young to remember the aristocratic Malcolm Macarthur’s criminal spree in 1982 may well have learned about it via contemporary Irish literature. A cultivated socialite whose days were devoted to refined leisure and the life of the mind, at the age of 37, Macarthur found himself in deep financial trouble. Frantic at the prospect of having to work for a living, he hatched the unlikely plan of carrying out an armed robbery. To do this, he would need a car and a gun. In the course of procuring these, he murdered – brutally, senselessly – two young people: a nurse named Bridie Gargan and a farmer named Dónal Dunne.

When the gardaí arrested Macarthur at the Dublin home of Ireland’s attorney general, Patrick Connolly, where he was hiding out as a guest, the scandal almost toppled Charles Haughey’s government. It also birthed an enduring acronym, “Gubu” (grotesque, unbelievable, bizarre and unprecedented), and fuelled conspiracy theories concerning the workings of class and power in a nation whose deep political corruption had not yet been exposed.

Fintan O’Toole recently revisited the Macarthur saga in his personal history of modern Ireland, We Don’t Know Ourselves, while John Banville’s indelibly sinister 1989 novel, The Book of Evidence, was inspired by the crimes. Now, Mark O’Connell, an acclaimed nonfiction author and Dublin native, has written an entirely singular book about this murderer who, we learn in its opening pages, was arrested in the same apartment block where O’Connell’s grandparents were then living.

As the author of two very fine books and plenty of superb journalism, O’Connell has found many admirers, of which I have long been one. A gorgeously nimble stylist, he writes the sort of sentences that get me checking my own in agitated competitiveness. More to the point, no contemporary literary mind seems to me more subtle, perceptive or trustworthy.

For all their obvious merits, those first two books – To Be a Machine, a dispatch on the transhumanist philosophical movement, and Notes from an Apocalypse, a travel-heavy meditation on the end times – frustrated me in certain ways. The writing was most vivid when it was intimately personal, yet I never quite believed in the “obsessions” of which the books were supposedly a working out. The trope of authorial obsession was a pretext for dark-tourist excursions and dutiful, journalistic engagements whose actual content – kooky apocalypse preppers and the like – was often only passably interesting, perhaps even to the author, whose centre they seemed to lead him away from. The inflated interest manifested, formally, as conventionalism. I kept wanting O’Connell to be an artist, and he kept settling for being a reporter.

With A Thread of Violence, such protests have melted away. The proof that, this time around, the author was truly pregnant with his subject lay in how spooked I felt even while reading it – which I did in the rising suspicion that one of my contemporaries has gone and written a masterpiece.

There are early hints that A Thread of Violence is to be something new and dizzying: a Borgesian true-crime story. Haunted by Macarthur’s “rare and strange form of abjection” as he roams Dublin’s streets (he was released from prison in 2012 after serving 30 years), O’Connell determines to find him and announce his intention of writing a book. Although Macarthur has turned down many previous invitations to speak to journalists and documentarians, he agrees to open up to O’Connell. The two men begin a series of long conversations, both at Macarthur’s inner-city home and on the phone, which provide O’Connell with the tissue of his eerie, philosophically probing book.

No sooner has this strange collaboration begun than O’Connell, who as a one-time PhD literature student thought extensively about John Banville and The Book of Evidence, finds that he has “wandered into a labyrinth of endlessly ramifying fictions”. Speculating that “reality itself was a niche subgenre of fiction”, and experiencing his encounters with Macarthur as “a tearing of the thin fabric that separated fiction and nonfiction”, O’Connell finds himself prey to the awed vertigo that an author – or a reader – might feel on suddenly grasping that he is already part of a book that is writing itself through him.

If I’m making it sound as if O’Connell has demeaned the gravity of his subject by deploying the bells and whistles of postmodernist meta-trickery, I assure you this is not the case. The conjuring of labyrinths and dark fictive mirrors enhance the book’s ghostly power and underscore its deadly seriousness. It reads like a seance with the spirits of the still-living.

Immaculately paced, A Thread of Violence generates a suspense that is formal and narratorial as much as it is a corollary of genre: we read it rapt with curiosity as to how the author will avoid the ethical pitfalls up ahead, how he can possibly pull this off without sensationalism or vulgarity. The moral murkiness of writing such a book at all is intrinsic to its architecture: there’s no getting around that, by fixing his attention on a double murderer, the prestigious writer effectively signs an endorsement on the jacket cover of Malcolm Macarthur’s life, declaring it darkly riveting, profound in its moral implications. Even the most sophisticated book will extend Macarthur’s infernal celebrity. O’Connell is only too aware of this, not least on being discomfited to realise he has been photographed by an onlooker while walking the streets with Macarthur: “Whether I liked it or not, I was implicated.”

Eschewing the jokes and stylistic brio of his earlier work in favour of a stark lucidity, O’Connell sees in the “highborn savage” Macarthur a grotesque mirror to his own upper middle-class privilege, and in his crimes an irreducible mystery that is indistinguishable from blunt mundanity. Resolved not to lose sight of the horror of what Macarthur calls his “criminal episode”, O’Connell nonetheless grants his subject a fair hearing, writing about the elderly murderer with, if not quite a redeeming empathy, a spooked and perplexed grace.

While Bridie Gargan and Dónal Dunne’s surviving family members declined to speak with O’Connell and presumably will not welcome his book’s publication, they may be reassured to know he could not have gone about all this with more care or decorum. A Thread of Violence instils the certitude not only that no one else could have written this book, but that no other need ever be written on the subject. It’s a marvel of tact, attentiveness, and unclouded moral acuity. I admire it without reserve.

Rob Doyle is the author of Threshold and several other books

• A Thread of Violence by Mark O’Connell is published by Granta (£16.99) in the UK and in Australia on 29 August. To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply