Tinker Tailor Soldier Spy (15)

As a film, Tinker Tailor Soldier Spy is a good read. What, after all, is John le Carré's novel about, if not reading? Early on in Tomas Alfredson's new adaptation, espionage veteran George Smiley pops into the optician to exchange his specs for a new pair – big, square, heavy-rimmed, instantly familiar as the sort worn by Alec Guinness in the revered 1979 TV adaptation. The scene plays sly homage to the actor who made the role his own – as Gary Oldman now makes it his own – but it also reminds us what kind of spy Smiley is. He's a reader, an analyst, and he needs those glasses because his job is to scrutinise the barely visible fine print between the blurry lines.

That's what Alfredson's film invites us to do: it offers ample pleasures, not least distinctive visuals and a feast of classy acting, but don't expect to get the best out of it unless you stay alert and bring your reading skills to the table.

Is the film difficult? It's not easy, and it doesn't intend to be. But part of the pleasure of Tinker Tailor is the anxious thrill of getting lost in its winding corridors. Like the novel, the film defies easy summing up. George Smiley (Oldman) is retired from British intelligence service "the Circus" – MI6 to you and me – but he's been recalled by the government to root out a mole, a double agent who's spilling Circus secrets to Russia. But Smiley and his lieutenant Peter Guillam (Benedict Cumberbatch) must do their job secretly, spying on the Circus itself. They must find their man by stealing files, winkling out semi-confessions, analysing a mountain of documents, dossiers and memos – which Smiley prefers to do by retiring to his personal reading room in a drab hotel.

Tinker Tailor is dense, deep stuff, and a mark of its subtlety is that the deceptively mild-mannered Smiley doesn't utter a word until 20 minutes in. One of the joys of the film is that Oldman, after years playing supporting heavies, has a real role to grapple with, and one of enticing complexity. His Smiley is inscrutably cerebral, seemingly committed to a cause that he can see right through; aware that his calling obliges him to betray the friends who are probably betraying him; and engaged, at long distance, with his own shadowy Moriarty figure in the KGB. Oldman conveys all this with impeccable reserve, while implying in his character a barely supportable weight of pain and tainted knowledge. His weary but ever correct delivery suggests tact, punctiliousness, the patience of a birdwatcher stalking a rare, possibly mythical species. He also reveals an unsuspected ferocity, even cruelty – watch him coolly terrorising a suspect on an airfield.

The performances are superb throughout, the actors obliged – because of the story's fast-shifting complexity – to convey a lot in a few deft strokes. Among them are Cumberbatch's nervous, eager Guillam, a suavely arrogant Colin Firth, Tom Hardy bullish as field operative Ricki Tarr, Toby Jones's dapper terrier of a Circus grandee, and John Hurt, magnificently cracking up as cantankerous, burnt-out spymaster "Control".

The script is a brilliant feat of condensation and restructuring: writers Peter Straughan and the late Bridget O'Connor realise the novel is overtly about information and its flow, and reshape its daunting complexity to highlight that. Audaciously, the film doesn't smooth over Le Carré's discontinuities, but gives us a string of self-enclosed anecdotes that we must collate for ourselves: Guillam's nerve-racking raid on a filing room, a brilliantly conceived Circus office party at which the star turn is a Lenin-faced Santa, and Tarr's ill-fated liaison with a Russian woman in Istanbul (the only moment at which the film resembles an action-laden spy thriller, because Tarr, narrating events, is writing himself a conventional Bond role).

Alfredson, the Swede who made the glacial vampire story Let the Right One In, is an unlikely but inspired choice of director, and visually re-imagines Le Carré's world from the ground up. Cameraman Hoyte van Hoytema and designer Maria Djurkovic create an ominous atmosphere, more grey than noir, not parodying the styles of the decade but suggesting that 1970s London wasn't that different in mood or look from 1950s Prague.

As for the Circus, its dusty London office is recast as a vast, impersonal space, something between a small parts factory and an antiquated British film studio. Its meeting rooms are mounted in soundproofed industrial containers, in which neatly buttoned officials huddle at the table like Oxbridge dons: you expect them to pass port anti-clockwise as they conspire. You're reminded of the closed universe of the Stasi, as depicted in the German film The Lives of Others: despite the "us and them" myths of the Cold War, Le Carré's fiction reveals how utterly alike the two sides are.

The film makes you realise, too, the danger and perniciousness of Smiley's world. There is more overt violence here than in the novel – a slaughtered corpse in a bath, passers-by as collateral. We realise, for all the urbane protocol and tweedy formality, that we're looking at a dirty business that suits a dirty world order. Nearly 40 years on from the novel, the fading into memory of the Iron Curtain adds the bitter edge of futility to these characters' desperate, obsessive endeavours.

Editor Dino Jonsäter manages the intricacy superbly, making you feel you've entered a dark, enclosed labyrinth. A key image is a shot of railway points shifting and connecting – a metaphor for Smiley's mental processes, and for the ever-mobile complexity of the narrative. You'll feel your own synapses working at full tilt as you watch this intelligent, bracing, consummately achieved entertainment.