Tomas Alfredson’s immaculate John le Carré adaptation, Tinker Tailor Soldier Spy, may be the unsung masterpiece of the 2010s. After garnering a few nominations on the awards circuit and lately making a handful of best-of-the-decade lists (including FilmFisher’s), it seems destined to pass unseen from the public consciousness. This lack of fanfare is sad, though unsurprising, and perhaps appropriate. With its nigh-impenetrable labyrinth of a plot and its mood of studied stillness, the film is as undemonstrative as the lonely, broken souls who inhabit its bleak Cold War world, yet it grows more engrossing with each viewing. Its obstinate refusal to hold viewers’ hands is an invitation to watch closely, keenly, patiently, poring over each oblique frame for hidden meaning like George Smiley (Gary Oldman), the rare movie hero who watches far more than he acts or speaks. Early in the film, Smiley – forced out of the British secret service and into a solitary retirement – is fitted for a pair of new glasses, which come to represent the detached perspective that allows him to peer into the Circus from outside, in search of a Russian mole. The scene at the optometrist’s office clues us into the central role that sight will play in the drama of the film, for Smiley’s glasses both aid and isolate him. “You’re rather well placed to look into the matter,” a civil servant tells him. “Outside the family, as it were.” The more removed Smiley is, the more he can see. As ill-fated Jim Prideaux (Mark Strong) puts it, loners are always the best watchers.

Underneath all of the methodical, intricate spycraft, the film turns out to be nothing more or less than a tangle of tragic love stories, and intense quietude finally gives way to bombastic pathos with a closing montage set to “La Mer,” Julio Iglesias’ French rendition of “Beyond the Sea” –which is, of course, a love song. This montage is Tinker Tailor Soldier Spy’s world in microcosm. By looking closely at it, one can see the entire mosaic of the film falling into place.

“La Mer” (the sea) is a fitting image with which to close the film: it conjures Odysseus as the cunning Smiley returns home to his own long-lost Penelope, suggests the unnavigable expanse (of secrets, time, death, or the Iron Curtain) that separates other sets of lovers from one another, and evokes the internalized depths in which the characters have spent the film submerged, scuttling Prufrock-like across the floors of silent seas. Lest it seem that I am reading too deeply into the choice of song, notice that the montage begins in (and thus, the music is coming from) the film’s third flashback to the Circus’ Christmas party, and that each flashback is accompanied by a musical cue that clues us into the film’s emotional undercurrents. The Christmas party is the point where the film’s sexual and political intrigues overlap, and as such, it holds the key to the film’s mysteries. The first flashback shows Smiley wishing his wife, Ann, a Merry Christmas, just before Bill Haydon (Colin Firth) wishes Prideaux the same. The roomful of spies is singing along to Sammy Davis Jr.’s parodic “The Second Best Secret Agent in the Whole Wide World” – a brutally appropriate choice, as Smiley and Prideaux will both be playing second best before the night is out. In the second flashback, the national anthem of the USSR plays while Smiley sees his wife seduced by Haydon, who has himself been seduced by Soviet spymaster Karla. (Also heard, briefly: Charlie Rich’s “The Proudest, Loneliest Fool,” which begins with the line, “She didn’t see things my way…”)

The montage begins in the moment when Prideaux first perceives Haydon’s duplicity. Even at a Christmas party, Prideaux is lurking in a darkened corner by himself. Likely isolated because of his closeted homosexuality, he is watching, rather than joining in; elsewhere, he remarks to Bill, a student at the boys’ school where he teaches, “You’re a good watcher… us loners always are.” (Round-faced, bespectacled Bill bears something of a resemblance to a very young Colin Firth, and he surely reminds Prideaux of another Bill.) At the Christmas party, Haydon saunters through the crowd and makes eye contact with Prideaux from across the room. He is holding two glasses, but declines with a wordless smile when Prideaux makes a subtle pass; the other glass is for Ann, who he is about to debauch at Karla’s behest. Prideaux’s eyes narrow slightly, concernedly, as if he is not sure how to interpret what he has just seen, though Smiley concludes that, “deep down,” he knew about Haydon’s treachery all along. Prideaux’s love blinds him, preventing him from acknowledging what he knows, but it is this suppressed awareness that unconsciously drives him to warn Haydon before embarking on a mission that could expose the Soviet mole in the Circus, and so his love is precisely what gets him captured and tortured by the Russians.

The montage jumps ahead to another exchange of glances, as Haydon catches sight of Prideaux looking at him through the scope of a sniper rifle and seems to blithely accept his death. Then again, Haydon does nearly everything blithely; Firth plays him as a hollow man whose thin, mask-like smile never betrays a hint of genuine happiness, and whose sexual promiscuity both reflects and disguises his ideological promiscuity. Haydon is virtually the only character in the film who even bothers to pretend to be genial, but he is surely pretending, and in his final scenes, he plumbs new depths of miserable emptiness. (“It’s just a reaction… an overreaction, if you like,” he says of his own tears.) Strong, who is often stuck with the thankless duty of playing one-note villains in blockbusters, works wonders whittling away layers of Prideaux’s brawny stoicism to unearth a sad tenderness. His murder of Haydon should be a crime of passion, a jilted lover’s revenge, but Strong plays it so resignedly it could be a mercy killing. It is young Bill who bears the brunt of Prideaux’s feelings: “Just bloody join in, will you?” he rages after learning of Haydon’s betrayal, but the outburst is directed not at either Bill so much as himself and his own life of lonely watching. When Prideaux shoots Haydon from afar, they are looking at each other and at the camera, but after Haydon’s death, Alfredson shoots Prideaux in profile: alone again, the line of sight broken. A tear of blood falls down Haydon’s cheek and its saline twin runs down Prideaux’s.

The montage cuts from the falling tears of Haydon and Prideaux to a downpour of rain drenching Ricki Tarr (Tom Hardy) at the tail end of his own doomed romance. Although Tarr is outside in the cold, the shot is framed such that he might as well be inside a cage, behind bars like Haydon, imprisoned by his unfulfilled longing for a lover who will never return. Tarr, like Prideaux, has fallen in love while watching; on assignment in Istanbul, he spies Irina (Svetlana Khodchenkova) through a pair of binoculars. Though he is supposed to be surveilling her husband from afar, Tarr inches closer and closer to the window as the scene goes on, his vision narrowing in on Irina, and he subsequently breaks protocol by initiating an affair. Tarr describes their “holiday romance” as a ruse to get information, but Smiley seems to suspect, as we do, that his motives run the other way: the romance is what Tarr really wants, and the information is the ruse that lets him deny it to himself and his superiors. Hardy, known for his loud, showy performances, dials it back for Alfredson, yet still has the most demonstrative face in the lineup. Everyone else is intensely buttoned-down, but as Tarr, Hardy is barely holding it together, telling Smiley about Irina like a high schooler who has just fallen in love for the first time and is shattered by the idea that such a thing could happen to him. “She wasn’t even my type,” he blusters, teary-eyed and trying to laugh it off, at once desperate to disclose his feelings and terrified of compromising his credibility by revealing the true depth of his investment. Smiley, fixated on his own buried loyalty to an absent woman, sees right through Tarr, persuading him to help unmask Haydon by agreeing to try and get Irina back from the Russians – an empty promise, for we have already seen her unceremoniously executed in front of Prideaux. (It is unclear whether or not Smiley knows.) The truth drains Tarr’s final actions of any catharsis, leaving him utterly disillusioned with the life of a spy by the film’s end: “I am out. I want a family, thank you… I do not want to end up like you lot.”

The next shot juxtaposes Tarr’s jaundiced view of the Circus with the nostalgia of Connie Sachs (Kathy Burke). Both characters are “outside the family,” like Smiley at the beginning of the film, but here, Alfredson frames them as foils for each other. While Tarr has chosen to leave the Circus, and we are looking out at him through a window, Sachs has been forced out of the Circus against her will, and we are looking in on her through the window of her home. Sachs is something of an outlier in the film, a willfully blind woman amid a cadre of watchful men, and while Tarr rails at Smiley and the others for having no families, Sachs lives at home, surrounded by adolescents who we assume are her relations – a setting not unlike Prideaux at the boys’ school. Yet this seems to be no antidote for loneliness. An old woman surrounded by youth, Sachs pines for the past and “all [her] lovely boys” at the Circus. We learn she was dismissed for “losing perspective,” peering into matters where her eyes were not wanted – a drama that plays out in miniature when she mentions Smiley’s separation from Ann and he quickly steers the conversation back to business. Rejected from the insular world of the Circus and pushed out into “the real world,” Sachs withdraws into self-imposed blindness, mulling over idealized memories of the good old days. “That was a good time, George,” she sighs, and when he demurs – “It was the war” – she replies, “A real war. Englishmen could be proud then.” Sachs does not want to lose the illusions of past happiness among which she dwells. “If it’s bad,” she tells Smiley, “Don’t come back. I want to remember you all as you were.” It’s bad, of course; this line from Sachs cues Smiley’s first flashback to the Christmas party, as he begins to probe into the past, seeing through the nostalgia – a process of demystification that ends with Haydon’s corpse. In the final montage, Alfredson cuts from Sachs, stewing in her memories, back to the sad reality: one of her “lovely boys” sprawled in a bed of leaves. The reflection of leaves on Sachs’ window links the images, almost as if she is looking (or pointedly not looking) at Haydon, remembering him as he was.

Yet for all its sadness, the film ends rather happily for Smiley himself, as Alfredson cuts from the bloody denouement of one romance to the unexpected restoration of another. We first see Smiley walking up to the door of his flat, where he has previously met two unannounced guests: first it was Tarr, seeking his help to get Irina back, and then (in flashback) it was Haydon, trying not to let on that he spent the night in Smiley’s bed with Ann. In both cases, Smiley’s personal life is being invaded by his professional life, for Haydon is only sleeping with Ann on Karla’s orders as a ploy to pull the wool over Smiley’s eyes. Smiley is more vulnerable at home than at work, more perturbed by domestic affairs than by international espionage, and Oldman’s performance is such a masterpiece of restraint that we cannot help attending to his most infinitesimal losses of composure – both of which (there are only two) have to do with Ann. Witnessing her liaison with Haydon at the Christmas party, he gasps, turns away, steadies himself against a wall, and adjusts his glasses. Like Prideaux with Haydon or Tarr with Irina, Smiley’s love for Ann challenges his ability to see, and her infidelity jeopardizes his role as a detached observer. When he pushes his glasses back into place, they are no longer implements that help him see but shields that protect him from pain and mask his weakness. (Alfredson often frames Smiley with his glasses catching the light, keeping us from seeing his eyes.) Smiley refuses to look at Ann because it hurts too much; Karla exploits this blind spot to keep him from seeing Haydon straight and deducing that he is the mole. In a touch befitting the film’s oblique nature, both Karla, its main villain, and Ann, the hero’s love interest, are faceless and voiceless – Smiley can neither see nor hear them clearly, no matter how much he tries. (Perhaps he has forgotten Karla’s face because it pains him to remember their meeting, in which he revealed himself to his nemesis, making Ann a target.) The second time Smiley loses his composure, he is returning home to find a third unannounced guest in his flat: Ann, from whom he has been separated since before the film’s beginning. She is out of focus at the end of the hallway, and we only see Smiley’s back as he leans against the banister to steady himself for a moment before descending the stair to lay a tender hand on her shoulder. Unlike Prideaux, Smiley forgives his faithless beloved and welcomes her home.

In Tinker Tailor Soldier Spy’s world, professional and personal lives are always bleeding into each other, and so the restoration of Smiley’s home runs parallel to the restoration of the Circus. After spending the film “outside the family,” he is welcomed back, ascending to take his place at the head of the table. The closing image’s mood of quiet triumph is shaded with bittersweetness, though, for the Circus’ yellow control room has been emptied of bureaucrats, traitors, and friends alike. Smiley is finally safe because he is finally entirely alone. The applause that closes out the recording of “La Mer” is ironic, for there is no one left to applaud.