At an awards dinner, Eve Harrington—the newest and brightest star on Broadway—is being presented the Sarah Siddons Award for her breakout performance as Cora in Footsteps on the Ceiling. Theatre critic Addison DeWitt observes the proceedings and, in a sardonic voiceover, recalls how Eve’s star rose as quickly as it did.
The film flashes back a year. Margo Channing is one of the biggest stars on Broadway, but despite her success she is bemoaning her age, having just turned forty and knowing what that will mean for her career. After a performance one night, Margo’s close friend Karen Richards, wife of the play’s author Lloyd Richards (Hugh Marlowe), meets besotted fan Eve Harrington in the cold alley outside the stage door. Recognizing her from having passed her many times in the alley (as Eve claims to have seen every performance of Margo’s current play, Aged in Wood), Karen takes her backstage to meet Margo. Eve tells the group gathered in Margo’s dressing room—Karen and Lloyd, Margo’s boyfriend Bill Sampson, a director who is eight years her junior, and Margo’s maid Birdie—that she followed Margo’s last theatrical tour to New York after seeing her in a play in San Francisco. She tells a moving story of growing up poor and losing her young husband in the recent war. Moved, Margo quickly befriends Eve, takes her into her home, and hires her as her assistant, leaving Birdie, who instinctively dislikes Eve, feeling put out.
Eve is gradually shown to be working to supplant Margo, scheming to become her understudy behind her back, driving wedges between her and Lloyd and Bill, and conspiring with an unsuspecting Karen to cause Margo to miss a performance. Eve, knowing in advance that she will be the one appearing that night, invites the city’s theatre critics to attend that evening’s performance, which is a triumph for her. Eve tries to seduce Bill, but he rejects her. Following a scathing newspaper column by Addison, Margo and Bill reconcile, dine with the Richardses, and decide to marry. That same night at the restaurant, Eve blackmails Karen into telling Lloyd to give her the part of Cora, by threatening to tell Margo of Karen’s role in Margo’s missed performance. Before Karen can talk with Lloyd, Margo announces to everyone’s surprise that she does not wish to play Cora and would prefer to continue in Aged in Wood. Eve secures the role and attempts to climb higher by using Addison, who is beginning to doubt her. Just before the premiere of her play at the Shubert in New Haven, Eve presents Addison with her next plan: to marry Lloyd, who, she claims, has come to her professing his love and his eagerness to leave his wife for her. Now, Eve exults, Lloyd will write brilliant plays showcasing her. Unseen but mentioned in dialogue, Karen has begun to suspect Eve as a threat to her own marriage to Lloyd, and so she and Addison meet for lunch and help each other put the pieces about Eve together. Addison is infuriated that Eve has attempted to use him and reveals that he knows that her back story is all lies. Her real name is Gertrude Slojinski, she was never married, and she had been paid to leave her hometown over an affair with her boss, a brewer in Wisconsin. Addison blackmails Eve, informing her that she will not be marrying Lloyd or anyone else; in exchange for Addison’s silence, she now “belongs” to him.
The film returns to the opening scene in which Eve, now a shining Broadway star headed for Hollywood, is presented with her award. In her speech, she thanks Margo and Bill and Lloyd and Karen with characteristic effusion, while all four stare back at her coldly. After the awards ceremony, Eve hands her award to Addison, skips a party in her honor, and returns home alone, where she encounters a young fan—a high-school girl—who has slipped into her apartment and fallen asleep. The young girl professes her adoration and begins at once to insinuate herself into Eve’s life, offering to pack Eve’s trunk for Hollywood and being accepted. “Phoebe”, as she calls herself, answers the door to find Addison returning with Eve’s award. In a revealing moment, the young girl flirts daringly with the older man. Addison hands over the award to Phoebe and leaves without entering. Phoebe then lies to Eve, telling her it was only a cab driver who dropped off the award. While Eve rests in the other room, Phoebe dons Eve’s elegant costume robe and poses in front of a multi-paned mirror, holding the award as if it were a crown. The mirrors transform Phoebe into multiple images of herself, and she bows regally, as if accepting the award to thunderous applause, while triumphant music plays.