This is an extraordinary time for Irish fiction. I know, it’s nearly always an extraordinary time for Irish fiction. But one of the things that’s striking about this particular extraordinary time for Irish fiction is how many of its leading figures – Anne Enright, Kevin Barry, Claire Keegan, Colin Barrett – keep getting better and bolder.

Rónán Hession is probably best known for his 2019 debut Leonard and Hungry Paul, the charming, compassionate tale of two men in their 30s who are yet to throw a starting six in the Snakes and Ladders game of life. There are characters like Leonard and Hungry Paul in his third novel, Ghost Mountain, and plenty of the same deadpan wit. But it’s a much more ambitious book – ambitious to an almost comical degree. The whole thing could be read as one brilliant riff on Sam Goldwyn’s famous request that a story start with an earthquake and then build.

Ghost Mountain opens with what should be a seismic event: the sudden, unexplained appearance of a mountain on the edge of an unremarkable town. “Emerging from the surrounding unfamous landscape, it was higher than all around it, though not very high.” As major geological disruptions go, its immediate impact is pretty muted. The mountain is discovered by a woman called Elaine, who is out walking her dog. For various reasons, it takes a few days for the news to get out. Once announced, the mountain attracts flocks of tourists, disrupts the routines of the town, wins admirers and enemies.

For the Clerk of Maps, it’s the opportunity of a lifetime, a chance literally to put something on the map. The town drunk finds himself drawn into this task, and therefore becomes less drunk. The landowner on whose property the mountain appears can’t figure out what to do with it, or his tenant. Ocho, one of the central characters, becomes a kind of Ghost Mountain widower, as his wife is more and more bewitched by it. The mountain becomes the thing against which everyone is measured. Like a pandemic or a war, it casts its giant shadow, but even in the shadows life continues. People get on with having children, starting school, being injured by falling theodolites – and so on.

In lesser hands, you could see this turning into some sort of cute parable about how we lose sight of the wonder in our lives, or whatever. But, despite its magical appearance, the mountain feels real. Hession is brilliant at framing the minutiae of ordinary days and feelings – the way a child at school can be drawn to another because he says “shit in a bag”. Perhaps it’s because, like Chekhov or Magnus Mills, Hession did not give up the day job (he is assistant secretary general of Ireland’s department of social protection, as well as being the blues singer Mumblin’ Deaf Ro). And, after all, mountains do seem to appear and disappear. I say this as someone who once sat with a map on his knee in Murrisk, County Mayo, trying to figure out the location of Croagh Patrick, before turning round to see it just a few yards behind me, slipping off its cloak of cloud.

The book is written in a series of short chapters that skip between characters and sometimes make big leaps in time. Each chapter feels fresh and surprising, without being disorienting. At one point we hear that there are other unexplained mountains in other towns, including the Weeping Mountain. Ocho goes to visit this wonder, but his main impression is of a lot of mud and a striking contrast between the dampness of the air and the dryness of his peanut butter sandwich.

As the novel goes on, characters come into sharper focus – we eventually get to know the town drunk’s name. But the precision and purpose of the word “unfamous” in that first description of the mountain should tell you all you really need to know about how good Hession is, and what he’s about. In ways sometimes delightful, sometimes funny, sometimes shocking, he uses the inexplicable mystery of the mountain to show that our own lives are every bit as inexplicable and mysterious as any magic mountain. His story starts with an earthquake, and builds down to an entrancing whisper.

• Ghost Mountain by Rónán Hession is published by Bluemoose (£18). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply