“George Smiley returns!” proclaimed David Sexton in the London Evening Standard. In John le Carré’s 21st novel, his iconic spook, whose last fictional outing was a quarter of a century ago, makes a somewhat improbable appearance (he must be more than 100 by now). It is often a mistake for novelists to revive favourite characters late in their careers, but here, “remarkably”, le Carré (pictured) pulls it off. Complex and “ingeniously layered”, A Legacy of Spiesshows that, even at 85, Britain’s greatest thriller writer hasn’t “lost his touch”.

This is a novel for “le Carré aficionados”, said William Boyd in the New Statesman. Set in the present day, it is narrated by Peter Guillam, Smiley’s loyal number two, and it looks back more than fifty years to the operation at the centre of the author’s most famous novel, The Spy Who Came in from the Cold: the infiltration of a British agent, Guillam’s friend Alec Leamas, into the Stasi, the East German spy service, and his ultimate sacrifice. In 2017, Leamas’s son has sued the government, seeking damages and an apology. And Guillam is duly summoned out of retirement, from his farmhouse in Brittany, to be interrogated by MI6. To follow the novel’s elaborate plot, you “have to be on your intellectual mettle”; but that, as ever, is part of the pleasure. Though not quite “seamlessly excellent” – le Carré sometimes “gets the tone of the contemporary world wrong” – this is a “gripping” read.

A Legacy of Spies is “riveting”, agreed Andrew Marr in The Sunday Times. “The plot, interleaving events of the early 1960s with today, is deft and fast moving.” A topical bonus is that Smiley’s reappearance reminds us “just how Europeanist le Carré’s world always was”. Like his creator, Smiley is an “avid reader of German literature”, and it was “European political failures and European political compromises” that drove him. And in this novel, when Guillam finally tracks him down, Smiley reveals where his loyalty lies; “I’m a European, Peter,” he declares. “If I had a mission – if I was ever aware of one beyond our business with the enemy, it was to Europe.”

It’s good to be back in le Carré’s world, said Andrew Taylor in The Spectator. He has the unique ability to turn “bureaucratic gobbledygook and departmental slang into something approaching an art form”. But is A Legacy of Spies in the same league as his best novels? “The answer is no, of course not.” It’s haunting, fascinating and “finally unsatisfying” – a novel, perhaps, with “the air of a swansong”.