Tomas Alfredson's film version of John Le Carre's spy classic brings intelligent, understated thrills.

For the spies who work in the Circus, the inner circle of Britain's secret intelligence service, information is rarely simple. It can be hard to come by, it can be hard to decode and it can be even harder to contextualize. These spies don't rappel down the sides of buildings or romance beautiful women, they deal in the grey murk of disinformation and counter disinformation. The small, insignificant details are often what end up meaning the most.

The same goes for anyone watching Tinker Tailor Soldier Spy, the adaptation of John Le Carre's classic spy novel. The film, with a script by Bridget O'Connor and Peter Straughan, is purposefully opaque, and replicates the experience of reading Le Carre. I usually spend the first 40 or 50 pages of a Le Carre novel slightly lost, unsure of who the characters are or why I should care, but eventually everything snaps together in a moment of clarity. The same thing happens with the film version of Tinker Tailor; it's deliberately paced up front, introducing characters and locations and concepts with a brusqueness that could throw off audiences. But those willing to pay good attention during the first thirty minutes - to approach this film like the Circus approaches information, sifting for every bit of signal in the noise - will soon find everything clicking into place, and a subtly thrilling story unfolding before them.

Informed by the real life MI5 mole Kim Philby, the events of Tinker Tailor involve a highly placed Soviet double agent. One of the most trusted members of the Circus is the mole, but which one? George Smiley, forced into early retirement, is tasked with rooting out the mole before all of the intelligence gathered by the West is undermined.

Tinker Tailor is a cold, subdued film, but because it is so filled with information and because it is so reduced from Le Carre's original work, it almost gallops along. Director Tomas Alfredson never stops the film to highlight a bit of information or to make sure we make a connection; he keeps his steady pace going, trusting that we are always one step behind him.

We are, and we are helped along by the exquisite performances Alfredson coaxes from his excellent cast. Gary Oldman is riveting as Smiley, a spook with all the sex appeal and excitement of a desk clerk. Smiley is one of Le Carre's great heroes, with two sequels following Tinker Tailor, and I would love to see Oldman continue on as the spy with the English reserve.

Less reserved is Tom Hardy as Ricki Tarr, a field agent whose love affair with a Russian operative's battered wife opens the mole investigation. Hardy plays a character who is much more rough and tumble, a wetworks man who is just as comfortable slitting throats as he is seducing wives. The genius of the story is that Tarr, a sensualist and womanizer - about the best candidate to be turned by the Soviets - is at the center of it all, and he's relegated to sleeping on Smiley's couch as the investigation deepens.

John Hurt appears briefly - often in flashback - as Control, the head of the Circus who loses his job when an Eastern Block mission goes disastrous. Control believes that it was a mole in the Circus that gave them away, and after he dies he tasks Smiley with uncovering who it could be.

Smiley is the spy. Tinker, tailor and soldier are the other members of the inner Circus circle. Ciaran Hinds has a physical menace to him, Toby Jones is the weasel whose allegiance seems to only be to himself, David Dencik is the pawn, too ready to be used, and Colin Firth is the smooth operator, the one with any resemblence to James Bond. If James Bond worked in a dim, open plan loft space, that is.

Finally there's Benedict Cumberbatch as Guillam, a mid-level spook caught up in all of it. It's Guillam who offers the most viscerally exciting moments of the film, and I felt that the paranoia of the situation was most palpable coming from Cumberbatch, who sort of resembles a serpent.

Then there's Karla. The specter of Russian spycraft personified, Karla is the Soviet counterpart to Control. There are opportunities to show Karla, but Alfredson resists them; Le Carre's ultimate commie spook remains in the shadows.

The ending of Tinker Tailor is rather limp, a problem it shares with the book; fidelity has its drawbacks. But for Le Carre it isn't always the conclusion that excites, it's how you get there, and Tinker Tailor Soldier Spy winds through the tweed labyrinth of 70s British intelligence in a way that will enthrall the engaged viewer.

Best of all is the feeling of veracity. Le Carre knew people in the intelligence world, and the characters he created and the scenerios he sketched feel very much like they're pulled from actual files. Tinker Tailor is an immersive experience, with characters speaking in jargon and making references that aren't always clear to us in the audience. But it doesn't matter because it's all part of the glorious zeitgeist - murky, unsure, muddled and always so very, very grey. Maybe these things didn't happen, but they're all true.