The Author's surname is propitious. Her subject is the heart; its secret rules and reasons. Damage, her devastating first novel, starts with a whole, relatively stable man and shows him torn apart by romantic obsession. The Truth About Love, her sixth, tells the inverse story: how the heart heals.

The first chapter is disorientating, a gabbling stream of consciousness. Gradually we realise we are in the mind of a mortally wounded child. "Oh Mama, I feel all cold and wet..." He has been injured by a blast from his chemistry set; quite how a young lad might have come by such unsafe materials is never fully explained, but dark hints about the IRA rebound through the book.

After his excruciating death his family and neighbours take over the narrative, passing on the baton of his memory. The story isn't what compels you: it's the writing. Hart's dialogue is extraordinary, blending poetry and naturalism like the great Irish playwrights. "Coffee? No, but thank you. We're not great coffee drinkers. We don't want stimulants, you see. We want oblivion."

You don't read this book so much as hear it in your head. Indeed, you wonder if it began life as a radio play. The modern Irish greats – Brien Friel, Sean O'Casey – come to mind. Then Hart distances herself, interpolating dry little comments about the Irish from a stranger's perspective: "They all talk like this. It's their gift, their armour."

There is an expatriate's double vision at work, a perception of Ireland from within and without. The explosion stands in, poetically, for other bombing outrages, briskly listed later: 21 killed in Birmingham, 29 in Omagh.

Deceptively dreamy and emotional, this book has some sharp things to say about Irish nationalism. "The majority, what was the phrase? 'Condemn utterly what is happening, this barbarity.' But that's all we did. Condemn. And march. But not often enough. ... Did the dead stop us from bringing the South to a total standstill? To say, as they say nowadays, 'not in my name'".

There are points when this feels like an inadequately novelised memoir. But a book about accepting loss must start with a bang, and end with a whimper. Along the way there is much to relish, from Hart's elliptical epigrams ("There is always a secret between couples, and sometimes within it lies the seed of their destruction") to chapter five, a wonderfully meandering conversation between two men playing chess.

Unlike the tight chamber piece f Damage, this book is sui generis: a social-emotional history. Ireland's "economic miracle" is touched on, and the after-effects of 9/11 (one character gets a phone call: "It's over, Olivia... Try raising money for the boys back home in a New York bar now.") Philosophical asides are left dangling off the ends of paragraphs: "And as they always do, in time people forgot, though forgetting is an elective process." The final impression is of a dishevelled novel, rough-edged like burrs that catch in your mind and don't let go.