NOTE: This spoiler was submitted by David G

London, 1957: Ada Harris (Lesley Manville) walks along the streets at night and stops on a bridge. She takes an unopened package addressed to her out of her purse and wonders aloud to her absent husband Eddie if it will be “good news or bad?” She flips a coin, but it falls off the bridge.

Ada catches the bus the following day and tells the attendant that today is her lucky day. She sits with her friend Vi (Ellen Thomas). They both go to their jobs as cleaning women. Ada works at her clients’ homes, Mr. Newcombe (Christian McKay), a womanizing bachelor, and Pamela Penrose (Rose Williams), a messy actress. At night, Ada and Vi visit a bar and have a drink with flirtatious Archie (Jason Isaacs) before he is pulled away by a younger woman. Ada opens the package and finds Eddie’s wedding ring and a note saying it was recovered from a crash site near Warsaw. Eddie has been declared killed in action. Ada returns to the bridge and tosses Eddie’s ring into the river.

Ada works for Lady Dant (Anna Chancellor), a complex woman obsessed with status; Ada attempts to ask for her unpaid wages, but Lady Dant deflects. While putting items away, Ada becomes enchanted by a £500 Dior dress laid out in a room and is told to hide it away as Lady Dant wants to keep it a secret from her husband. At home, Ada bets on football matches and wins. She celebrates with Vi and decides she will buy a Christian Dior dress from Paris with her winnings once she makes enough. She starts walking to work to save money and asks her clients for referrals for more work. Pamela laments how hard it is to worry about her looks and how lucky Ada must be to not have to. Archie asks Ada to watch his date’s dogs while at the bar, and she calls herself an “invisible” woman. Ada asks Lady Dant to settle her account again, but Lady Dant deflects once more and says she has to reduce Ada’s hours.

Walking home, Ada finds an expensive diamond clip on the street and turns it in to the police. Archie invites Ada and Vi to watch the dog track races where he works. Ada bets on a dog named “Haute Couture” despite long odds, believing it to be a sign, but the dog comes in last place, and she loses all her money. Archie consoles Ada saying he appreciates that she’s a dreamer. The following day Ada is visited by a military man who says Ada is owed a significant payment as a war widow. The police also show up and tell the owner of the diamond clip Ada found wants to pay her a reward. Lastly, Archie shows up and says he knew her bet was terrible and put her money instead on a different dog that won. All in, Ada now has £582 pounds.

Ada flies to Paris, planning to go there and back in one day after buying the dress. She spends the night at Gare du Nord station, and a homeless man offers to show her the way to the Dior shop in the morning. Ada learns the streets of Paris are covered in garbage because the sanitation workers are on strike. At Dior, a throng of paparazzi surrounds the entrance. Still, Ada manages to get inside by helping a harried young model bring a bag inside. Confused, she tries to follow a group of guests into a fashion show but offends Claudine Colbert (Isabelle Huppert), the directress of Dior, by calling her a shopgirl. She meets Andre Fauvel (Lucas Bravo), a Dior accountant. She is invited into the fashion show by the Marquis de Chassagne (Lambert Wilson) as his guest. Marguerite (Roxane Duran), a Dior employee, runs backstage and tells the models, including Natasha, about how Ada has saved all her money to visit and see the show. Madame Avallon (Guilaine Londez), a snobby guest, refuses to sit next to Ada, but there are no other options. The Marquis instructs Ada to write down the dress number she likes and wants to buy, but Madame Avallon overhears and chooses to buy the same one. Andre offers to give Ada her second choice, which she agrees to but panics when she learns the dresses will take two weeks to be custom-made. Natasha arrives and tries to help with the problem; Andre offers to let Ada stay in his sister’s home while she is out of town. Andre is eager for Ada’s all-cash sale because Dior has fallen on hard financial times.

Ada is brought to the fitting room and measured for her dress; she charms everyone with her kindness. Natasha drives Ada to Andre’s sister’s apartment, and they drive past the sites of Paris. Natasha helps her into the apartment and helps her clean it up as Andre’s sister is a slob. Andre shows up with groceries, and Ada cooks them all dinner. Natasha and Andre bond over their love of existential philosophy. Natasha says she wants to be seen as more than a beautiful face. At the next fitting, Marguerite explains that Claudine is rude because their high-paying clientele does not pay for their garments until delivery and that Dior is experiencing financial pressure currently as a result. Ada runs into them, and he takes her to a flower market and invites her out that night. The two visit a burlesque theater show, where they run into Natasha, who is there entertaining Dior investors. Ada drinks a lot of champagne and oversleeps the following day. She races through the streets of Paris and shows up late to her fitting, where Mr. Carre, the tailor, refuses to do any further work on her dress, and Claudine says there is nothing to be done. Marguerite, feeling sorry for Ada, takes her to see the atelier. Ada says it feels like she’s gone to heaven.

Claudine finds Ada working as a seamstress in the atelier and is upset. Claudine explains that Dior serves only the best clientele. Still, Ada has upset the normal process, and the staff wants to complete her dress. Claudine mocks Ada for not having a suitable place to wear the dress. The Marquis sends flowers to Ada and invites her out for tea. Ada and Andre stroll along the Seine, and he tells her more about Dior’s financial woes. Andre explains he has some ideas to help the business, but Claudine refuses to accept them. They stumble upon a red-carpet movie premiere where Natasha is acting as the arm candy for the leading actor. Andre is hesitant to say hello, but Natasha greets them both. Andre asks Ada to stop trying to set him and Natasha up even though he is in love with her; Andre suggests Ada attend to her own heart.

Ada visits the Marquis’ home for tea. The Marquis explains that he felt an immediate kinship with Ada because she reminded him of a maid that worked at his boarding school when he was a child. She “gives comfort to those in need without asking anything in return.” Ada is heartbroken that she reminded him only of the help, not a romantic partner, and leaves. Ada goes to Dior the next day and learns that many staff has been let go due to budget cuts, and others are striking outside. Ada rallies the entire staff and goes to speak with Christian Dior (Philippe Bertin) as Claudine protests. Ada explains that Andre has ideas to save the company, and Andre speaks up to say that Dior should make some goods available to all consumers. Christian agrees to Andre’s suggestions; the new plan will include hiring everyone back, so Claudine walks out of the room, conceding defeat.

Ada and Andre visit Claudine at her home and discover she lives in a modest apartment where she takes care of her infirmed husband, wounded in the war. Claudine understands the new direction but no longer wants to work at Dior. Still, they convince her the company will fall apart without her, and Claudine agrees to stay on. Claudine tells them that Natasha has left Dior and Paris, so Ada and Andre go to the train station to chase her down. They find Natasha, who says this life on a pedestal is not for her. Andre and Natasha kiss, and he asks her to stay in Paris.

Ada returns to Dior, and they finish making her dress. Ada returns home to London. Her client Pamela Penrose shows up at her door upset. She asks Ada to help remove a stain on the dress she would wear to an event, but Ada says it will be too difficult. Pamela says she has no other options, so Ada offers her the Dior dress. Ada goes to Pamela’s home the next day and discovers the dress has been severely damaged. She reads a note left behind by Pamela that the dress was accidentally lit on fire. Still, Pamela is not apologetic, and Ada quits. Ada takes the damaged dress and tosses it off a bridge into the Thames. Ada refuses to answer, knocking at her door, so Vi and Archie break in to check on her. Vi consoles a despondent Ada. Ada returns to Lady Dant’s home and learns that the story of Pamela setting the Dior dress on fire has made the news. Lady Dant laughs about the story, so Ada quits and tells Lady Dant she can no longer treat her like scum and that she requires complete payment.

That night, Ada receives a delivery of a giant package and a bouquet of flowers. She opens the box and discovers a new custom-made dress in the style of the dress number she originally wanted. There is a note from Claudine, Christian, Andre, the Marquis, and Natasha explaining they saw the news in the paper and realized Ada had once again been too kind, thinking of others first. They tell her that Madam Avallon’s husband was arrested for not paying his workers, so their assets were frozen, and the dress she had claimed can now go to Ada. The note says sales have increased thanks to her involvement, and they wish her well.

Ada wears the Dior dress to a dance at the Royal British Legion dance with Vi, and she stuns the crowd as she makes her grand entrance. Archie comments that something about Ada has changed and that she’s always been beautiful. The two of them dance.