The Temporary Gentleman is Sebastian Barry’s third novel to mine the McNulty family history. This time the protaganist is Jack, brother to Eneas from The Whereabouts of Eneas McNulty, and brother-in-law to Roseanne from The Secret Scripture, the woman who was “disappeared” into the local asylum by the creepy new zealot of a priest, Father Gaunt. Gaunt went on to confiscate her baby, as was shockingly commonplace in Ireland during the first half of the 20th century and continued right up until the 1980s. Jack believes that Roseanne subsequently died of TB, so thorough was the system in its obliteration of all traces of her - again, a scenario not uncommon in Ireland at the time. People - usually women - who did not fit in with the strict Catholic morality were bundled off into institutions, never to be heard from again. It happened to a relative of Barry, his great-uncle’s first wife, prompting him to give her a life and a voice. The Secret Scripture went on to win the Costa book of the year award, came close to winning the Man Booker prize, and is being made into a film starring Vanessa Redgrave and Jessica Chastain, who will play old and young Roseanne, respectively.

The gentle, reverent and almost archaeological manner with which Barry set about excavating Roseanne’s secret history is reminiscent of the manner in which W. G. Sebald charted the lives of similarly displaced and traumatised souls. Barry shares with Sebald a fascination with the upheaval of war and its effect on those uprooted by it. Indeed, it was a war novel that first brought Barry to international prominence. A Long Long Way (2005) was narrated by Willie Dunne, a young Irishman who enlists in the British army to fight for the rights of small nations in the first world war, only to find himself fighting not just the Germans but his own people during the Easter rising in Dublin in 1916.

Barry returns to the topic of war with A Temporary Gentleman. Jack McNulty, the narrator, may not be a blood relative of Willie Dunne, but he is forged of the same steel. The title of this, Barry’s eighth novel, is a pejorative term used to refer to someone who may be considered, through rank for example, a “gentleman” for the duration of a war. Jack, also an Irishman, enlisted as an engineer in the British army when the second world war broke out. The novel opens in 1957 with Jack, now “a balding, ageing Irish ex-major”, unable to face returning home to Sligo, finding himself instead “lurking in Africa like a broken-down missionary”, having been posted there during the war. Why can’t he face going home? Guilt. The novel is an exploration of his guilt.

Jack sits in his African cottage jotting down memories of his dead wife. He hopes that by setting down his recollections, he will return to Ireland “a better man, a mended man. That is my prayer now.” This text within a text is a device Barry has employed before to great effect, but, despite the familiar technique, the narrative agency is a departure. To date, Barry’s novels have been narrated by good people, vulnerable people, people who are trammelled by others, but Jack is largely culpable for the damage that befalls those close to him.

During his student days in University College, Galway, he meets fellow student Mai Kirwan, a “woman replete, laden with gifts, musical, athletic, clever as a general”. Unlike Jack, she is from a wealthy background, and he knows she is out of his league.

Mai’s beloved father promptly spots Jack’s drink problem and is horrified by the match. When her father dies, Jack - fully aware that “the loving thing to do” would be to “show her the mercy of silence” - takes advantage of her grieving state to propose to her. Mai accepts with the word “alright”. The novel tracks her subsequent downfall. She inherits her father’s mansion. Jack gambles and drinks it away. Mai, in much diminished circumstances, falls prey to what would now be recognised as postnatal depression. Jack enlists in the army, largely to escape, and Mai takes to the bottle.

I will put my hand up and confess to having had a fleeting “change the record” moment with Barry’s last novel, On Canaan’s Side, only to be bowled over by the unexpected power of the ending (so many writers have tried and failed to capture the moment of death). The states of goodness that his previous narrators maintained in the face of startling iniquity were beginning to strain belief, but then, Barry’s writing is inspired by his family so it is natural to write with tenderness. The Temporary Gentleman, however, is narrated by the bad guy. Jack is a drinker, a gambler, an absent father, a neglectful husband, a gunrunner and, at the end, a coward, afraid to return home. The hallmark heightened lyricism and stylised idiom of old is still there, but it is tamped down by Jack’s rueful voice.

The novel seems part of something bigger, almost a prelude, in fact; and this is not a flaw but, rather, an indication that new life is being breathed into the Barry project. Watchers have been planted within the text in the shape of Jack and Mai’s two unfortunate daughters, Maggie and Ursula. They are almost entirely silent: terrified children in an adult world, witnesses to misery and - in one vicious episode - subjected to violence. They appear at windows, or at the top of stairs, observing their parents’ abject state as they drink themselves into oblivion. Their presence is electric, because you know that it is only a matter of time before Barry will get round to telling their stories. Maggie, the oldest, becomes an actor, locating her in his immediate familial terrain: his late mother was the actor Joan O’Hara. Ursula emigrates to England to become a nurse, fearful that her father will disapprove of her engagement to a Nigerian. The novel ends as Jack’s testimony ends, having succeeded in intriguing the reader. If anything, the work is getting more exciting as it broaches contemporary times.

Barry is drawn to complicated subjects. He has not shied away from illuminating the ugly side of Irish nationalism, the hypocrisy of religious divides - but is there anything more complex than a family? And is there anything more impossible to pin down? Some writers grasp the topic by the neck, stun it into submission with clever observations and wry remarks - Jonathan Franzen’s The Corrections springs to mind - as if omniscience of individual emotional landscapes were an available option. It takes a writer of the stature and delicacy of Barry to recognise that you could dedicate your entire working life to the endeavour and still expect the resultant novel to be hopelessly partisan and partial. Yet in the act of sifting through versions, of setting down words, you might excavate some facet of the human heart that casts light on what it means to be alive. It is Barry’s steadfast devotion to this process that makes him an artist of the highest order.