After the end of the cold war and the various extremely warm ones that followed it, the classic spy novel –and what other kind is there? – came to seem increasingly an anachronism. There is a generation of people approaching middle age who never knew what it was to live with the always astounding yet incontrovertible fact that life on earth could and might well be obliterated at any moment, not by the action of God or the gods, but by the handiwork of humankind itself. The international conflict that began in the wake of the attack on the twin towers is random and internecine, and our fear of it is febrile and unfocused; cold war fear was not worse, just different, a concentrated, dull, ashen sensation that one could almost feel between the lips, like a coating of radioactive dust.

John le Carré was a connoisseur of that brand of terror; all his spies lived with it at every moment, waking and sleeping; it was the kind of grit that caused pain but produced no pearl.

Indeed, one of the main sources of Le Carré’s enduring popularity – he has been a bestselling author for more than half a century – was the palpable grittiness of his books. No matter how entertaining they were, they purveyed harsh truths about the world, insisting we face up to the fact that behind the facade of quotidian reality, forces are at work that are more real than the majority of us wish to acknowledge. As Alec Leamas (the spy who came in from the cold) explains to his lover, the naive communist Liz Gold, the dirty game of espionage is carried on “so that the great moronic mass that you admire can sleep soundly in their beds at night”.

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With the collapse of European communism and the delusional period of peace that followed – we did not know what was slouching towards us out of the desert lands that had been the cradle of civilisation – a number of foolish book-chatterers predicted the end of Le Carré’s career as a novelist, since his great subject had collapsed overnight, like the tumbling down of a once seemingly permanent concrete wall. Of course, he went on to prove the pundits to have been wrong, as usual, with richly inventive works such as The Night Manager and The Constant Gardener. However, many readers pined for the good old days of the Circus, with its moles and lamplighters, its joes and scalp-hunters, its tinkers, tailors, soldiers and spies; its, above all, George Smiley. Well, they can stop pining. A Legacy of Spies brings it all back, as fresh and as rancid as ever, in a tale that shows the master in the full vigour of his old mastery.

From the start – even before The Spy Who Came in from the Cold, Le Carré’s third novel – he displayed a genius for plotting. With most crime or spy stories, we come to the end of the book and the plot with an anticlimactic thud, and the same feeling of dull vacancy we have when we complete a crossword and are overcome with the guilty sense of having squandered precious time and taxed our brain cells wastefully in pursuit of a trivial end. In the case of a Le Carré novel, even though plot is central to the book’s effectiveness and a main component of the aesthetic pleasure it offers us, we are aware of being addressed – admittedly in prose that is rarely more than workmanlike – by a real writer, one with a formidable intelligence and a highly developed moral sensibility. Although Le Carré would probably not claim to be an artist, his work, at its best, operates at a high literary level.

A Legacy of Spies – the title suggests more than one meaning – satisfies not only by being vintage Le Carré, which it is, but in the way in which it so neatly and ingeniously closes the circle of the author’s long career.

Peter Guillam, Smiley’s former right-hand man, is long out of the Service and enjoying a bucolic retirement in Brittany, in the village where he was born to a Breton mother and an English father who fought bravely behind the lines in France before D-day, and died a hero’s death at the hands of the Gestapo. Peter was brought up in England, but never lost his Breton French, or his love for his native place. One day his peaceful idyll is disturbed by the arrival of a terse letter, ostensibly from one A Butterfield at 1 Artillery Buildings, London SE14, summoning him immediately to England in connection with “a matter in which you appear to have played a significant role some years back”.

In London, Guillam presents himself dutifully, and apprehensively, at the Secret Service’s “shockingly ostentatious new headquarters” on the Thames. Here he is greeted by a pair of lawyers, the bouncing Bunny, “a fresh-faced, bespectacled English public schoolboy of indefinable age in shirt sleeves and braces”, and Laura, short-haired, 40‑odd and menacingly businesslike.

Facebook Twitter Pinterest Benedict Cumberbatch as Peter Guillam in Tinker Tailor Soldier Spy (2011). Photograph: Allstar/Focus Features

This long early scene, in which the veteran Guillam spars and feints with the pair of latter-day technocrats, is Le Carré at his gleefully contemptuous best. Not the least of the pleasures here is the accuracy with which Bunny’s Essex accent is captured with its steely, fake chumminess and random emphases: “Peter! Gosh! You look positively jaunty! And half your age! You travelled well? Coffee? Tea? Honestly not? Really, really good of you to come. A huge help.”

What has happened, we learn, is that the grown-up offspring, a son and a daughter, of, respectively, Leamas and Gold, have emerged from the shadows threatening a profoundly embarrassing and ruinously costly joint court action against the Service for having been responsible for the deaths of their parents. In its defence, the Service must go back and delve into the operation that formed the plot of The Spy Who Came in from the Cold, and which ended with the deaths of Leamas and his lover on the wrong side of the Berlin wall. Guillam, as a surviving key player in the ostensibly lost chess game, is required to tell all he knows about the affair, and give a plausible account of his involvement in it, or else: Guillam, we are reminded, in one of Le Carré’s typically laconic and chilling throwaway lines, “draws full pension and [is] therefore torturable”.

The plot of the new book is derived from and intricately woven into that of its predecessor. This is an immensely clever piece of novelistic engineering, of which its deviser can be justifiably proud. The ingenuity and skill with which the thing is brought off is breathtaking – really, not since The Spy has Le Carré exercised his gift as a storyteller so powerfully and to such thrilling effect. He has had to make a few tiny tweaks to the original narrative to ensure a plausible fit for the new one. For instance, Karl Riemeck, the agent who dies at Checkpoint Charlie in The Spy, undergoes some adjustments here; also, the time-frame in which A Legacy plays out is necessarily vague, since Smiley, who was already a spy in the second world war, is still alive – though mum’s the word on that, so as not to spoil the sport.

Smiley still uses the end of his tie to wipe his spectacles, through which he still stares at people owlishly – true, he is a bit of a cliche, but it is a pity that the cliche was set in stone by the television portrayal of him by Alec Guinness, an actor who by strenuously underplaying managed to overplay wildly. Smiley is “Le Carré man” in essence: a reluctant “cold warrior”, impossibly clever, wise to the world’s wickedness yet unshakeably decent at heart. And since this is probably the last – brief – encounter we shall have with him, he should be accorded the last word.

It is a particularly apposite word, in these increasingly isolationist, chauvinistic times. Wondering what it was they fought for, he declares a sort of enduring faith: “I’m a European, Peter. If I had a mission – if I were ever aware of one beyond our business with the enemy, it was to Europe. If I was heartless, I was heartless for Europe. If I had an unattainable ideal, it was of leading Europe out of her darkness towards a new age of reason. I have it still.”

Is he an anachronism? Perhaps: but affirmatively, gloriously so.

• John Banville’s new novel, Mrs Osmond, is published next month.

A Legacy of Spies is published by Viking. To order a copy for £18.50 (RRP £20) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.