Since 1903, when Erskine Childers warned of the rising tide of German militarism that preceded the first world war in The Riddle of the Sands, spy fiction has enthralled and chilled its readers by holding a cloudy mirror to the murkier corners of international politics. During the Cold War, John le Carré’s novels were hugely influential in shaping popular perceptions about the private manoeuvres behind the public antics. His books have continued to explore the dark places of the world we live in, their subject matter evolving with the headlines.

Agent Running in the Field — an intentionally ambiguous title, no doubt — is le Carré’s 25th novel. The first and most important thing to say is that it’s a cracker. There was a whiff of weariness about his previous book, A Legacy of Spies, but here he writes as a man refreshed. Perhaps it’s an unexpected Brexit dividend.

During the course of the story, the Brexit negotiations grind on with no hint of a happy ending. President Trump pays his visit to Britain and continues to Helsinki, where he cosies up to Putin. The government of the United Kingdom is entrusted to ‘a minority Tory cabinet of tenth raters’. Sound familiar?

Nat, the narrator, is a 47-year-old SIS officer, who has spent most of his professional life running agents in hostile countries for the Russia Department. Like many Le Carré protagonists, he’s the product of a disjointed and fractious upbringing. He’s also a fitness fanatic, which he combines with an impressively steady intake of alcohol. Now on the verge of retirement, he’s back in England and hoping to rebuild his family life. But the Office persuades him to take a temporary assignment running the Haven, a redundant London substation, staffed with agents past their sell-by date.

Nat’s wife Pru, a lawyer with a conscience, is less than enthusiastic, but she doesn’t stand in his way. To confuse matters, Nat’s newly recruited deputy at the Haven is Flo, an unsettling young woman who bears the stamp of Cheltenham Ladies’ College.

The narrative is framed as a debriefing: as though Nat is making a rambling statement to his superiors in the wake of an unknown disaster.  It opens with a badminton game at the club near his Battersea home. Nat, having just won the club championship, is challenged by a gauche young stranger named Ed. Spread over weeks and months, their games punctuate the story. Gradually an unexpectedly close, though uncomfortable, relationship develops between the two men: neither father and son nor agent runner and agent, but with elements of both. Ed, a researcher, emerges as determined, earnest and endearing. He believes that Brexit ‘in the time of Donald Trump’ is ‘an unmitigated clusterfuck bar none’.

Meanwhile, Nat’s superiors are intriguing behind his back, sleepers are waking from their slumbers and old agents are tumbling out of the woodwork. Someone appears to be feeding the Russians with details of the government’s more explosive post-Brexit contingency plans.

Many of Le Carré’s novels explore the nature of loyalty, but here he gives it a different twist. The result is a rich, beautifully written book studded with surprises. Narrative is a black art, and Le Carré is its grandmaster.

It’s true that the plot depends on a coincidence of epic proportions, and that some episodes verge on the implausible. But this is an emotionally complex story, not an exercise in probability: what really matters is that we invest in the characters and we care what happens in their lives.

I doubt I’ll read a better thriller this year.