Plot: Thomas Leroy, the artistic director of a New York City ballet company, is mounting Swan Lake as the company's next production. Many of the ballerinas in the company aspire for the lead, which would have previously gone to the company's former principle dancer Beth Macintyre before her forced retirement. No one wants the the role more than Nina Sayers, who lives to dance, so much so that she wants to be exactly like Beth in every aspect. Nina lives with her overbearing mother, Erica Sayers, a former ballerina who now lives vicariously through her daughter as she never made it as a ballerina herself. Nina is a technically proficient and hard working dancer who can easily capture the essence of the innocent white swan, but Thomas doesn't believe she has the dark passion required to portray the black swan. An unexpected move by Nina convinces Thomas that Nina may have what it takes, and he gives her the lead. Thomas will do anything to get that passion out of her. Nina feels that her new place in the company is threatened by Lily, a ballerina newly arrived into the company from San Francisco. Lily, who is looser in every aspect of her life than Nina, encompasses the essence of the black swan more so than Nina. But as Nina believes Lily is to her what she herself was to Beth, Nina, in doing whatever it takes to be perfect as both the white swan and the black swan, descends into madness.
Alternative Plot: Nina (Natalie Portman) is a ballerina whose passion for the dance rules every facet of her life. When the company's artistic director decides to replace his prima ballerina for their opening production of "Swan Lake," Nina is his first choice. She has competition in newcomer Lily (Mila Kunis) however. While Nina is perfect for the role of the White Swan, Lily personifies the Black Swan. As rivalry between the two dancers transforms into a twisted friendship, Nina's dark side begins to emerge.