Brandon (Michael Fassbender) is an addict. His drug is not heroin, cocaine, meth, or alcohol, but sex. Although he can function in social scenarios, he’s hindered by uncontrollable urges, and his only fix is to have an orgasm. He needs this many times a day just to get back up to normal. Several shots of his face throughout the film make it clear that the sensation has long since stopped giving him pleasure. One near the end, for example, which captures the moment of climax, reveals despair and self-loathing. For him, sex has nothing to do with intimacy, love, or even physical satisfaction; it has become a burden that consumes his every waking moment. There’s no room left for anything else in his life, not even for something as ordinary as feeling emotions.

With Shame, director Steve McQueen makes no grand statements about sex addiction. He merely observes what the characters do. They reveal themselves primarily through their actions. When they do speak, there are no sermons that sound uncannily like a written monologue; there are only simple, direct conversations. Most are quiet, as when Brandon has dinner with an office employee named Marianne (Nicole Beharie). Why does he pursue her when he has access to prostitutes, who demand nothing from him other than payment? Perhaps he thought he could have a go at a conventional relationship. But he’s not wired that way. He isn’t all that interested in what she says, nor is he all that interested in saying things to her.

He makes a comfortable living in a Manhattan office building. His exact job title is never revealed, which is just as well because work is not foremost on his mind. Several times a day, he excuses himself to the men’s room so that he can masturbate. His chatty, energetic boss, David (James Badge Dale), is married and has a family, although that doesn’t stop him from barhopping and hitting on women with a slew of pickup lines. He usually brings Brandon along; he sits impassively saying barely a word, and yet women are more drawn to him, perhaps because David is simply trying too hard. The irony is, Brandon is not seeking their affections. Even amongst large groups of people, it’s obvious that he has nothing resembling a social life.

Into his life reenters his sister, Sissy (Carey Mulligan), a wayward young woman who needs a place to stay. As of right now, she gets by as a lounge singer; we will eventually hear her sing what is arguably the saddest rendition of “New York, New York” ever, and indeed, a mostly uninterrupted shot of her face shows nothing but solemnity (when it cuts back to Brandon’s face, we see a tear rolling down his cheek). Her visit is jarring for Brandon, who has isolated himself with his addiction. He doesn’t want anyone to see the porn on his computer, or his hidden stash of dirty magazines, or his masturbation sessions in his bathroom. In other words, he doesn’t want anyone to see his shame. When she crawls into bed with him, he immediately screams at her to get out. He doesn’t care that she needs the support.

Scenes late in the film suggest the possibility that Brandon is inching closer towards human feeling, that he’s finally allowing himself to care about something. But the possibility of staying the way he is remains just as strong. At one point, he’s so desperate for a fix that he enters a gay night club. This has absolutely nothing to do with orientation; when your sole purpose in life is achieving orgasm, who you’re physically attracted to is not taken into consideration. His background is just as shrouded in mystery as Sissy’s, although hints at something dark are dropped along the way. Sissy will eventually deliver a key line: “We’re not bad people. We just come from a bad place.”

This year alone, Fassbender has appeared in films as diverse as Jane Eyre, X-Men: First Class, and A Dangerous Method. In all three, he gave great performances. But I think his appearance in Shame will be the one that stands out the most. Rather than project dramatically, he retreats to an inward, solitary place where emotions go to die. As Brandon, he’s walled off and yet extremely vulnerable. No matter how many people he’s surrounded by, his is a world of pain and loneliness. In one pivotal scene, he’s travelling by subway, staring at a woman who may be flirting with him; his eyes betray not malice intent but sad desperation, for he knows, even in the throes of his physical urges, that he has put himself into a repetitious cycle of destructive behavior. As to whether or not he’s doomed to stay in it, there are some things we’re never meant to know.