With the task of playing Smiley, one of the most beloved characters in all of spy fiction, Gary Oldman makes the wise decision to build upon Guinness' portrayal rather than reinvent it. Guinness was famous for taking a part (whether Smiley or Obi Wan Kanobi) and paring his performance down more and more, removing as much expressivity as possible. What is somewhat amazing about Oldman's performance is that he is able to make Smiley even more stately, even more minimal than Guinness. His slow, quiet, terse movements and speech set the tone for the rest of the film, which allows major twists and turns to be communicated via subtle touches. The changes in Smiley's eye ware are sometimes the only clue we have to flashbacks, for example. Everything is as buttoned up and controlled as Smiley--or Oldman's performance of him.
Smiley, however, like the Circus itself, is not what it seems and the conceit of the film is that the paranoia brought about by a mole is always already embedded in the very fabric of spying itself. The spies not only monitor the Russians (and everyone else in the Easter Bloc), but each other as well. The British are caught between the glare of the American cousins, whom they despise and want to impress at the same time, and the Russian counterparts, symbolized by their infamous leader, Karla, who dogs their every movement. Everyone looks for everyone else's weakness, and the spectre of a mole simply further personalizes the search. That is, spies are not just human, but more so. Their very humanity makes them vulnerable.
In the film as in the novel, the danger for the agents is personal feeling. In the novel, Le Carré makes it clear that it is personal relationships that the British secret service is good at, while the Americans, weak on this front, are good at technology. Yet it is in the supposed superiority of their contacts and their sources that leaves the British vulnerable as it is false intelligence that ultimately causes the British to fall for a trap that convinces the Americans that they are receiving invaluable information on the Soviets and thus should entrust the British with their secrets. The mole, however, takes the American information and passes it on to Moscow, which gives back only a sprinkling of information in return--just enough to make their false data seem reliable. This fool's gold that the British mistake for "treasure" not only makes them seem sloppy and endangers their operatives, but opens the Americans up to danger as well. Unwittingly, the British have harmed Western intelligence by their attempt to seem superior to the Russians and to curry favor with the Americans. Their 'feminine' position between the two super powers--trying to make a strength out of a weakness--opens them up to instability, no longer knowing what or who they are.
Le Carré's genius is to make this seeming personal weakness resonate not only with the Circus as a whole, but with Smiley's personal life. Deeply in love with his wife, Ann, the film flashes back to a drunken Christmas Office party in which Smiley sees Haydon smile at his wife. Later, outside, he sees her in his embrace. To his coworkers, Smiley is not only Control's right-hand man, but a cuckold whose personal life is a tragedy. Haydon assumes that it can be Smiley's distraction, his blind spot, that will keep him from ever seeing the mole. That Smiley is able to see through this occlusion, even use the knowledge of his wife's affair to his advantage in capturing the mole, is a testament to Smiley's control of his own emotions as well as his ability to rationalize the elaborate covert operation that has ensnared his agency in a deception that is so difficult to unravel.
Alfredson's version of the story brings out Le Carré's text via a variety of techniques. Not only is London rendered in stark tones, seemingly in decay much like a version of the future as Orwell might have imagined it, but portions of the novel are referred to without being spelled outright. Smiley talks about his encounter with Karla, which is shown in detail in the novel, by reenacting a conversation with him for Peter Guillam (Benedict Cumberbatch). Likewise, Smiley mentions giving Karla a pack of cigarettes, which Karla takes but then returns unused when he is returned to Moscow, without mentioning that Smiley hated American cigarettes, especially Karla's favorite Camels. The film, in other words, references much more than it shows, leaving many subtle hints to the novel's fans that appear in the film as depth and fullness, fleshing out a world that is much more than merely another spy tale, but a deconstruction of the genre itself--a sort of meta story in which the inner workings of a secret world become a metaphor for life as we live it, and die from it, and can never tell ourselves what is really happening.