Tim Winton and speculative fiction may seem an odd combination. His novels excel at the here and now, depicting lives at the margins, young love and young parenthood, violence at the hands of fathers. But the harsh beauty of the western Australian landscape has long been a presence in his work, and Winton has also long highlighted his country’s fragility in the face of climate chaos, and been fiercely critical of the exploitation of Australia’s mineral wealth. So the cli-fi premise of Juice, his latest novel, could be a perfect Winton fit.

Set in an unspecified future, some centuries from now, the book opens on a man and a girl driving across a landscape blackened by ashes. The hellscape is worthy of the Mad Max franchise, with slave colonies springing up from the parched earth like termite mounds. There are echoes of Cormac McCarthy’s The Road here, too, in the black dust thrown up by the vehicle’s tyres, and in the child passenger, observing everything with a mute wariness.

The pair pull up at an abandoned mining station hoping for shelter, only to find that someone has beaten them to it – a rough figure with a crossbow, who is mistrustful of strangers. What unfolds is a long night of story. Taken captive, forced to talk in exchange for water – indeed, for his life and that of the child – Winton’s protagonist seeks to explain himself to the bowman.

We come to understand where we are in time and climate. “The Terror” of societal collapse is generations behind us. After the equatorial regions became uninhabitable, the ensuing wars and mass migrations gave rise to untold further suffering. Now the remnants of human civilisation are clustered across the globe’s far northern and southern reaches. People mostly live in bleak “Associations”, held together by mutual dependency and recitations of “the Sagas”, parables of agony and endurance passed down by surviving generations.

Our narrator begins his tale with his boyhood on the plains north of Perth, at the limits of habitable terrain. His father long lost, he and his mother toiled together, bodies wrapped in cloth, faces smeared in protective “sun paste”, growing corn and tomatoes in sheds during the winter, bartering their harvests for turbines and batteries, scavenging for spares, retreating underground during summer to escape the certain death of heat fever.

At 17, he finds love with another teenager, Sun, who has come to the plains from “the City”. Soon, they have a child named Esther because – well, because it just wouldn’t be a Winton story without this early step-up into manhood. The young narrator’s real purpose, though, arrives when he is recruited into “the Service”, a secretive paramilitary organisation whose operations provide the novel’s main driver.

In Winton’s world, the rich live in clans. Gazprom and Amazon are now bloodlines rather than corporations – and they’re as venal and inbred as medieval European royalty. Their bunkers are fortresses, vast and armed: the first mission our protagonist describes is the storming of a tower far out in the ocean; his most fateful is a citadel of sorts, carved into the walls of a Utah canyon, deep inside Earth’s scorched zone.

Unlike in Kim Stanley Robinson’s 2020 cli-fi novel Ministry for the Future, which projects a coercive response to corporate greed, the violence here is not corrective, intended to bring the clans in line – it’s pure retribution. Their rapacity gave rise to centuries of misery, and the Service exists to rid the world of their stain. This is page-turning stuff, gripping and awfully gratifying. But Winton knows how to twist the knife – and how to turn it back on those who wield it.

The protagonist’s double life as a plainsman and agent of vengeance soon became unsustainable. He tells the bowman of the painful questions it raised about Sun’s origins, and his own too. Who was his father? Why did the Service choose him? He reveals the cruelty of the organisation’s methods: its operatives required to kill not just the clan heads, but also their children, their guards and servants.

Juice is a hefty book, in terms of pages and the future it sets out, and it keeps delivering. Sympathies move to the most surprising quarters. Perhaps the most affecting of the protagonist’s stories belong to the clans’ foot soldiers, and to the woman who entrusted him with the child. To reveal more would be a spoiler – suffice to say that Winton sees hope in reaching across lines that seem to divide.

He uses the bowman well as the listener to this tale. Mistrustful to the last, the man’s scepticism keeps the narrative driving onwards. Will he believe enough to spare the protagonist? Why should readers trust the man’s word either? Winton’s ending is a masterstroke, the heart-in-your-mouth final chapter one of the best things I’ve read in a long time.

• Juice by Tim Winton is published by Picador (£22). To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.