NOTE: This spoiler was submitted by L.
Nina Sayers (Natalie Portman) is dancing the Prologue to Swan Lake, a ballet in which a young woman is turned into a swan and can only be turned back by the kiss of her true love. A sorcerer appears and places the curse on Nina as she wakes up in her apartment. She begins her daily stretches and tells her mother about her dream. Nina mentions that the director of her ballet company promised to feature her more this season and her mother mentions that it’s been long enough.
Nina goes to the ballet studio and learns that Beth (Winona Ryder) the former head of the ballet is being put out to pasture. As a result, the director, Tomas Leroy (Vincent Cassel) is looking for a new face to feature the company. Tomas announces the first performance of the season to be a reworking of Swan Lake and he invites Nina and several others to a private session in order to choose the next Swan Queen.
Nina’s audition is interrupted by the late arrival of new dancer Lily (Mila Kunis). Tomas is not impressed by Nina’s performance as she failed to capture the sexuality of the Black Swan, despite her flawless performance as the White Swan. Nina goes home in tears and practices until she breaks her big toe nail. The next day, Nina visits Tomas in his office and tells him she’s been practicing and wants the role. He tells her that he decided to give it to another dancer, and then kisses her passionately. Nina bites him on the lip, which shocks and impresses him. She finds out later that she got the role of Swan Queen and is overjoyed.
She sees Beth have a meltdown in her dressing room and enters it once Beth leaves. She goes through Beth’s things and steals several items: nail polish, earrings, a nail file and lipstick. She then calls her mother from the bathroom and tells her that she won the part. When she leaves the bathroom stall she sees the word “WHORE” written on the mirror in red lipstick and she immediately starts wiping away the makeup, embarrassed and aware of the controversy around the decision.
Her mother orders her a big cake and cuts her a slice but Nina tells her that she can’t eat it. Her mother almost throws the cake out from anger but Nina takes a slice before going to the bathroom and trying to vomit.
As the stress of the role and her inability to perform get to her, Nina begins having visions of herself in black walking around, oftentimes filling in for Lily. Tomas holds an event with which he officially announces Beth’s departure and Nina’s rise as the Swan Queen. Nina goes to the bathroom to purge and is interrupted by Lily coming into the bathroom to take off her panties and use the bathroom. When Nina starts to leave, Lily asks her to stay but Nina gives her a weird look and leaves. A little later, Beth gets drunk and confronts Nina asking if she “sucked his cock” to get the role. Nina is offended and tells Beth that she didn’t have to. Tomas breaks up the argument and takes Nina to his place. He asks her if she likes sex and gives her a homework assignment: she must touch herself and get in touch with her sexuality so that she may better inhabit the role.
She finds out the next day that Beth threw herself into oncoming traffic. She pays Beth a visit in the hospital and sees Beth’s ruined legs. Disturbed, she leaves and goes home.
Nina wakes up the next morning and begins touching herself. As she really starts to get into it, she realizes her mother is asleep in the chair next to her bed and freaks out. She goes to practice and cannot get the passion into the performance. Disappointed, Tomas sends the other dancers home and dances as her partner, slowly moving his hands around her body and arousing her. After a deep kiss, he walks away from her telling her that is how he seduces her and that it should be the other way around with her performance.
Nina is left behind to practice and does so until Lily arrives and sees Nina drying her tears. They chat a bit and Nina tries to defend Tomas from Lily’s comments that he likes to sleep with his troupe. Lily realizes that Nina has a crush on Tomas and jokes about it but Nina gets upset and leaves. The next day Tomas asks her if she needs time off, upset that Lily came up to him and told him that he should cut Nina some slack. Nina gets upset that Lily did that and yells at her.
That night Nina’s mother suspects that Nina has scratches on her back and assumes that Nina has been hurting herself again like she used to when she was younger. However, before she can confirm it there is a knock at the door. She answers the door, talks quickly before closing the door. Nina demands to know who it is and sees Lily. She asks how Lily knew where she lived and Lily tells her she asked Tomas’ secretary. Lily invites her out and Nina leaves with her, despite her mother’s protests.
The two go out and have a crazy night with two guys named “Tom” and “Jerry.” Nina takes some of Lily’s drugs and they go to a club. When she is next lucid, she realizes she’s in the middle of having sex with a random person in a bathroom. She leaves and Lily stops her. They take a cab back to Nina’s. Nina’s mother is waiting for them and asks Nina what she was doing and Nina says “I was with two guys named Tom and Jerry and I fucked them both” with a laugh. Nina’s mother slaps her and Nina grabs Lily and runs into her room, barricading the door with a piece of wood. The two then proceed to have sex and as Nina orgasms she sees herself as Lily, which scares her. But the two continue before Lily says “innocent girl” and puts a pillow over her head.
Nina wakes up with a headache and sees she is late for work. She yells at her mother for not waking her and tells her that she plans to move out. When she arrives at the ballet studio she finds that Lily is Nina’s alternate for the performance, which enrages her. She asks about last night but Lily doesn’t know what happened to Nina after the club, but is flattered that Nina had a wet dream about her. Nina leaves uncomfortably. She begs Tomas to not make Lily the alternate, convinced that Lily is trying to steal the role. Tomas tells Nina that the only person trying to sabotage Nina is Nina and leaves her.
That night, Nina is practicing alone and the lights shut off. She walks around and sees a cloaked figure running around (the Sorcerer from the dream) and waders around, seeing Tomas having sex with Lily. Lily smiles and Nina runs, engrossed in her fantasy. She winds up in the hospital and returns Beth’s things. Beth takes the nail filer and stabs herself in the face several times, causing Nina to run home. Her mother’s creepy paintings start talking to her and Nina runs to her room. Her mother tries to get in but Nina slams the door on her hand, breaking it. She falls down and collapses.
She wakes up the next day, hours prior to the premiere of Swan Lake. Her mother has locked the room and told her that she called Tomas and told him that Nina was sick. Nina hits her mother and steals the door knob before leaving for the ballet. She arrives to find Lily prepared to take the role but tells Tomas that if she doesn’t take the stage, the troupe will be marred with controversy. She goes to the dressing room and gets dressed.
The first half of the performance, prior to the emergence of the Black Swan, is ruined when Nina is dropped by her partner. Tomas is enraged and during the intermission, Nina is attacked by Lily in her dressing room. Lily turns into Nina and the two fight. Nina pushes Lily into her body length mirror and uses a shard of glass to stab her. She hides the body and takes the stage as the Black Swan. She dances fervently and as she dances, she begins to transform into a large Black Swan on stage. She blows the roof and seizes the moment to kiss Tomas passionately, effectively seducing him with her movements. She then leaves the stage and goes to change when the real Lily arrives to congratulate Nina for her performance. Nina is shocked but slowly, the pieces fall into place. She touches her chest and sees a shard of glass embedded in it. She removes it and takes the stage as the White Swan. She leaps from the constructed hill as the White Swan does to kill herself and lands on the mattress. Tomas finds her and tells her that she was perfect in her performance and Lily freaks out when she sees the amount of blood coming out of Nina. Tomas frantically asks her what she did and Nina replies that she was perfect.