Plot
In 1956 Paris, a young orphaned girl named Madeline attends a Catholic boarding school with eleven other girls, taught by the strict yet loving nun Miss Clavel and fed by the passionate chef Hélène. Despite having neither a family nor money, Madeline maintains a positive, yet mischievous attitude.
One night, Madeline is stricken with appendicitis and taken to the hospital, where she undergoes an appendectomy. During her stay there, Madeline bonds with Lady Covington, the terminally ill wife of the school's board of trustees member, Lord Covington. Unlike her husband, Lady Covington cares deeply for the school and the girls, having attended herself as a girl. Lady Covington reveals she carved her birth name, Marie-Gilberte, into one of the dorm's bed frames and asks Madeline to find out if her name is still there. A few days later, when Madeline leaves the hospital, she learns that Lady Covington has died. True to her promise, she finds Lady Covington's name and adds her own.
Later, the Spanish ambassador purchases the property next door to the school and moves there with his family. While the other girls are smitten with the ambassador’s spoiled son Pepito, Madeline is irritated by the noise he creates while riding around on his Vespa, calling him a "Bad Hat". Shortly after the ambassador's arrival, Lord Covington announces the plans on closing the school following his wife's passing and selling the building. Miss Clavel, unnerved by Pepito's bothering her girls, attempts to make peace with the boy by giving his tutor, Leopold, a toolbox for him; however, her actions are unsuccessful as Pepito steals Madeline's drawing pad and vandalizes it during a field trip.
Pepito invites the girls to his birthday party, during which he unnerves them by showing a mouse and joking about killing it. Madeline, infuriated by Pepito's actions, gets into a physical fight with him and releases all of his mice, causing the girls' visit to be cut short. As punishment, Miss Clavel forces the girls to write lines the next day. While out on a daily walk later, Madeline accidentally falls into the Seine while standing on the ledge of a bridge going over the river. She is rescued by a stray Labrador Retriever, whom she names Genevieve. Genevieve follows Madeline to the school and the girls convince Miss Clavel, who has an allergy to dogs, to keep her.
Wanting to save the school from being shut down, Madeline enlists Pepito's help to sabotage Lord Covington's attempts to sell the property. During this time, the two become friends, but her efforts are ultimately discovered by Lord Covington, who initially blames Miss Clavel. Madeline tries to take responsibility for her involvement, though Lord Covington is unmoved by her apology or the motivation behind her actions (especially after she accidentally calls him "Lord Cucuface"). After leaving, he discovers Genevieve and, as revenge against the girls, turns her loose into the night.
The next day, Miss Clavel takes the girls to a circus in hopes of cheering them up and helping them cope with the loss of Genevieve. Madeline, blaming herself for what happened and fearing she'll have no place to go as an orphan once the school closes, decides to join the circus, hoping to make friends and find a home within the community there. After confiding in her best friend Aggie of her plans and making her swear not to tell, Madeline leaves the group and unintentionally stumbles upon Leopold, with the help of a trio of clowns known as "The Idiots", kidnapping Pepito, hoping to ransom him. While trying to intervene, she is abducted as well. Aggie confesses to Miss Clavel that Madeline ran away while Pepito's parents discover he's missing.
Madeline and Pepito manage to break free of their bonds and find a motorcycle. Madeline uses her hair clip to start it and Pepito drives them away, using his experience with his Vespa. The two are pursued by Leopold and the Idiots but Miss Clavel, who is driving in search of Madeline (finding and picking up Genevieve along the way), is able to cause The Idiots to crash into a lake. The police eventually arrive and arrest the kidnappers, while Miss Clavel, Madeline, Pepito, and Genevieve head back to the school.
Shortly after Madeline's return, Lord Covington arrives and shares that he's sold the property to the ambassador of the Uzbek Soviet Socialist Republic. Madeline realizes he wants to sell the school as it reminds him of his wife's passing. She empathizes with Lord Covington, sharing her experience of losing her own family and assuring him that Lady Covington is still with him and the school. Miss Clavel promises Madeline that they'll be together regardless of what happens. Lord Covington is moved by Madeline's words and sincerity, but regretfully tells her and the girls that there's nothing he can do as he's already sold the property. In a happy twist, the ambassador, also moved by Madeline, decides to back out of the sale and allow the girls to keep their school. The film then concludes with a montage of the girls, Miss Clavel and Genevieve attending a fair, accompanied by Louis Armstrong's "What a Wonderful World", and changes back to the book setting as the word "Fin" appears.
