Plot summary

Brandon (Michael Fassbender) is a successful, handsome thirty-something businessman living and working in New York City. Unknown to those who know him, he's struggling with a sexual addiction. On a subway train he flirts with a young woman (Lucy Walters) and she flirts back with him. She has a wedding and engagement ring on, and when they exit the train, she disappears into the crowd.After work, Brandon and his boss David (James Badge Dale) go out and meet three women at a club. Later Brandon has sex with the woman David was trying to pursue.When Brandon arrives home, he assumes a burglar is in his house but finds a naked woman taking a shower: it is in fact his sister Sissy (Carey Mulligan), a troubled young woman who has been left as damaged as Brandon by their troubled childhood, which is never completely revealed. Sissy tells Brandon that she has been living in Los Angeles for the past year and performing as a singer in local clubs. Having fallen on hard times, Sissy claims that she has no place to live and asks if she could stay with him for a while. Brandon reluctantly agreesThe next evening, Brandon and David watch Sissy singing a beautifully sad jazz version of New York, New York at a club. Afterwards, Sissy sits with Brandon and David at their table where she talks a little more about herself and her singing career before. After a casual talk over drinks, they all go back to Brandon's apartment. While Brandon checks his mail in the lobby, Sissy and David go up to his apartment. When Brandon arrives, he hears Sissy having sex with David through the bedroom door, in his bed.Brandon leaves his apartment and runs on the streets while listening to Bach's piano music on his earphones. Brandon comes back home and sees that Sissy and David are gone. He changes the bed sheets and quickly goes to bed. A little later that night, he is annoyed by Sissy who climbs into bed and wants to cuddle him. Brandon yells at her to go back to sleep on the couch and she leaves him alone.At work, Brandon then tries to pursue a relationship with his co-worker Marianne (Nicole Beharie), by flirting with her and asking if she would like to have dinner with him, and Marianne accepts. After having a casual and pleasant dinner at a local restaurant, in spite of the young awkward waiter (Robert Montano) interrupting them several times, Brandon resists making a move on Marianne. They part ways at the end of the dinner, and he goes home alone.Later that night, Sissy arrives at Brandon's apartment and accidentally walks in on him masturbating in the bathroom. She then finds his laptop open full of pornography. Through the laptop camera, a woman (Charisse Merman) is half-undressed, touching herself while waiting for Brandon. She says that he would love the two women to get it together. Brandon violently appears and accuses Sissy of spying on him and she storms out. Brandon then takes all of his pornography in his apartment, including his laptop, and throws everything out.The next day at work, he approaches Marianne and takes her to a lavish hotel room. In the bathroom, hidden from Marianne's view, he snorts a line of cocaine. They attempt to have sex but Brandon cannot maintain an erection. Marianne leaves, while he stays at the hotel room, feeling lonely and humiliated. Some time later, Brandon is seen having sex with another woman (Amy Hargreaves) in the same hotel room.When Brandon gets home, he watches cartoons on his TV set, and Sissy arrives and talks to him. He asks her where she was, and she tells him that she was with David. Brandon tells Sissy that David happens to be married, and Sissy says that she already knows, for David told her during their first night together. Brandon angrily tells Sissy that she must move out at the end of the week to look for her own place to live. She says that they are family and are supposed to help each other, but Brandon wants nothing to do with her because he says all she does is drag him down.Brandon then heads out and tries to pick up a woman at a bar (Anna Rose Hopkins), but ends up getting beaten up by her boyfriend (Chazz Menendez) after he insults him by telling him how he would pleasure her. Bruised and beaten, he tries to enter a nightclub, but he is denied entrance, as the party-goers look much younger than its usual crowd; in fact, they are probably underage, so the bouncer (Carl Low) insists that he can't get in that night. Brandon sees a gay bar across the street and enters it. As he walks through it, a man approaches and kisses him, then performs fellatio on him in one of the back rooms. Next, Brandon is shown entering a cheap hotel room occupied by two women (Calamity Chang and DeeDee Luxe). He ends up having sex with both of them at the same time.When he leaves, he sees that Sissy left a voice mail on his cell phone. He gets off the train he is on due to its being delayed by an implied suicide further up the tracks. He frantically calls Sissy but she doesn't answer, so he rushes home. When he gets there, Sissy is lying on the bathroom floor after having cut her wrists. She survives and he visits her in the hospital. When he leaves, he collapses and cries in the rain.Some time later Brandon is seen sitting on the train, going to work as usual. The same woman from the beginning sits across from him, only wearing her engagement ring. He tries to look away but she keeps staring at him and smiling... clearly flirting with him. She stands up to leave the train, expecting him to follow her like the last time. Brandon keeps looking at her, and before viewers can know if he is going to follow her or not, the screen cuts to black.THE END[