Charity Hope Valentine, a dance hall hostess at the Fandango Ballroom in New York, stands by the lake in Central park, waiting for her boyfriend, Charlie. When Charlie arrives, silently preening himself, she imagines the pick-up lines he might say ("You Should See Yourself"). Abruptly, and without a word, Charlie steals Charity’s handbag, pushes her into the lake, and runs off. Passers-by discuss the apparent drowning but do nothing, until a young man finally rescues her.
In the Hostess Room of the Fandango Ballroom, Charity tries to convince herself and the other dancers that Charlie tried to save her. Nickie, a fellow dancer, tells Charity, "You run your heart like a hotel — you've always got people checking in and checking out." The manager, Herman, reminds them all to get to work. In the Ballroom’s main hall, the dancers proposition their potential customers ("Big Spender"). Charity, having moved from denial to anger, vows she’ll never let a man take advantage of her again ("Charity's Soliloquy").
On her way home from work, Charity encounters several panhandlers. Unable to say no, she gives them all her money. Just then, film star Vittorio Vidal and his beautiful mistress, Ursula, rush out of the ritzy Pompeii Club, arguing. Ursula refuses to re-enter with Vittorio, so he promptly takes the only-too-willing Charity instead. Inside the club, everyone wonders about the girl on Vittorio’s arm (“The Rich Man's Frug”). Charity tries to steer him away from the subject of Ursula. She confesses she hasn’t eaten since breakfast, and faints on the dance floor. Vittorio brings her to his apartment to recover.
On Vittorio's bed, Charity miraculously regains her strength. She admits she’s a dance hall hostess, and Vittorio is charmed by her humor and honesty. Starstruck, Charity requests a signed photograph. When Vittorio steps out, Charity can’t believe her good fortune ("If My Friends Could See Me Now"). Charity and Vittorio begin to enjoy dinner together, but Ursula suddenly arrives, so Charity hides in the closet. She remains there all night while, to her dismay, Vittorio and Ursula reconcile ("Too Many Tomorrows").
The next day, Nicki and Helene are appalled that Charity failed to get more out of Vittorio, and the three girls vow to leave their thankless profession ("There's Gotta Be Something Better Than This").
Deciding she needs some cultural enlightenment, Charity visits the 92nd Street Y, where she gets stuck in a broken elevator with a shy tax accountant named Oscar. Oscar suffers a claustrophobic panic attack, but Charity manages to calm him down ("I'm the Bravest Individual"). Just as they’ve both relaxed, the lights go black and they desperately call out for help.
To Oscar and Charity's relief, the elevator resumes working. Oscar invites Charity to join him at his church, which meets under the Manhattan Bridge. The Rhythm of Life Church – a former Jazz club turned religion – turns out to be a thin veneer on hippie culture ("The Rhythm of Life"). A police raid breaks up the meeting. Traveling home on the subway, Oscar guesses that Charity works in a bank, and Charity goes along with his assumption. As they part, Oscar kisses her hand, dubbing her "Sweet Charity."
Charity and Oscar continue dating, and two weeks later, she still hasn’t told him what she actually does for a living. Nickie and Helene mock Charity’s idealism, but admit to fantasizing about the future themselves (“Baby, Dream Your Dream”).
At the amusement park in Coney Island, Charity and Oscar get stuck on a broken parachute jump ride. This time, Oscar is the calm one; he declares his love for Charity and they kiss (“Sweet Charity”).
On a slow night at the Fandango, Charity loses a customer to her new, younger co-worker, Rosie. Disgusted by the whole business, Charity quits. Wandering through Times Square, she considers her future ("Where Am I Going?").
Charity meets Oscar at a Mexican restaurant and admits that she’s a dance hall hostess. Oscar confesses he’s known for a week, having followed her to work one evening. He says he doesn’t care about her past and wants to marry her. Charity is relieved and elated ("I'm A Brass Band").
Charity’s coworkers throw her a farewell party at the Ballroom ("I Love to Cry at Weddings"). After the party, Charity and Oscar walk in the park, and Oscar announces that he cannot go through with the wedding; he is unable to stop thinking about the "other men." Their conversation grows animated and Oscar accidentally pushes her into the lake. Panicked, he runs off. Charity emerges from the lake and asks the audience, "Did you ever have one of those days?" Realizing that this time, she’s retained her bag and her money, she shrugs and reprises her opening dance. Charity strikes a playful pose and three neon signs appear: "And so she lived … hopefully … ever after.”