When Madeline and the girls go to New York to meet their culturally diverse penpals and celebrate Halloween, Madeline finds some mysterious spider earrings in her trick or treat bag which she traces to Miss Clavel's missing cousin Fifi, a famous radio star.
Madeline and girls visit Miss Clavel's cousin Fifi at the radio station for the Halloween broadcast and accidentally leave the microphone on as they tell a scary story about ants invading New York, which is broadcast "War of the Worlds" style all over the city, sending all of the metropolitan area into a panic.
The girls enter a cancan competition, but the intense practice schedule and concerns about costumes creates a problem: cliques. The girls break into groups and exclude and taunt each other until Madeline, with the help of two legendary cancan stars, has the job of helping the girls make amends in time for their final competition.
When Madeline's sinuses act up, Dr. Cohn suggests she go someplace warm, so Lord Cucuface sends the girls to Cannes. Not heeding Miss Clavel's warning, Madeline stays on the beach all day, and gets sunburned, so she's forced to stay inside. She is so lonely and bored, Lord Cucuface asks his director friends to bring their latest movies - and, on Madeline's suggestion, a contest - The Cannes Film Festival is born.
Madeline and the girls play matchmaker and are invited to be in the resulting wedding. However, Madeline's feelings are hurt when Pepito starts ignoring her, not knowing that he's being ruthlessly teased by his cousin Pablito for "liking a girl". When she learns the truth, she convinces them it's okay for them to be just friends.
Nicole is embarrassed when she is asked to read a letter from her aunt, and it is revealed that her reading skills aren't as developed as the other girls. It turns out that her aunt has sent tickets to her and the girls to go to Africa. With Lord Cucuface tagging along, Miss Clavel and the girls join Nicole's aunt for a safari. There, they meet a friendly little gorilla named Rosie, and thru her, Nicole learns that she shouldn't be ashamed of being a late bloomer.
Promising them a white Christmas, Lord Cucuface takes Madeline, her friends and Miss Clavel to the North Pole where Madeline finds the elves stricken with the flu, so she and her friends decide to help Santa get all the gifts ready in time.
While touring Versailles with Miss Clavel and the girls, Pepito disobeys a "Do Not Touch" sign, and leaves fingerprints of mud and chocolate on a priceless harpsichord. Pepito feels more and more guilty until Madeline finally convinces him to fess up and face the consequences.
When the pipes burst and the old house is closed for a plumbing overhaul, Madeline and the girls move into Lord Cucuface's lavish suite at the Ritz. While there, they help a lonely rich girl and a hungry homeless girl, and soon discover that they'd rather have each other's love than live an empty upscale existence.
When Miss Clavel brings in a "method" acting teacher to direct the girls in a play, Madeline is sure she will get the leading role. Disappointed when given supporting roles (as trees) Madeline and her friends plan to boycott the play, until Madeline discovers that even small part can be important and fun, and that the girl who won the lead really deserved the part.
Madeline and the girls help to reform an unhappy puppeteer in the Jardin de Luxembourg, who, because he never had the talent to be an opera singer, puts on marionette shows that twist the plots of classic fairy tales and disappoint children in the audience.
When Madeline gets a pair of new ice skates for her birthday, she becomes so obsessed with practicing her skating that she neglects all her other responsibilities and friendships, and finally finds that ice skating has become a chore rather than a fun hobby.
When Madeline and the girls go to Dr. Cohn for a physical, all the girls have grown several inches except Madeline, who has a dream that she will be Tom Thumb-sized for her whole life. In the end, she feels better when she discovers that Georgette, the tallest girl, has size issues as well.
When Madeline and the girls are given the opportunity to be high fashion models and meet the top designer Mme. Cliché, they are asked to wear creations made of cheese and discover that fashion is fickle and it's what's inside that counts.
After Pepito burps at the dinner table, his parents insist on sending him to etiquette school, where he is joined by Madeline and the girls. After they graduate, Pepito's unruly cousin Pablito tries to convince Pepito that manners are uncool, but Madeline helps Pepito see the light just in time for him to put on his best behavior during an event for the soccer star Pepe Pelota.
After Pepito and the girls go to see Harry Houdini's show, Pepito decides to create his own magic show at home, and puts poor Genevieve in danger. Houdini helps the children see how to use magic properly and shows them how to appreciate the gifts they were born with.
Madeline and the girls become extremely jealous when lovesick Genevieve falls in love with a neighborhood dog, but in the end, Madeline helps the girls realize that Genevieve has plenty of love to go around.
While touring Lord Cucuface's perfume factory in Grasse, Pepito finds a friendly skunk, which he sneaks into the factory. When Chloe, offended by the skunk's odor, dips it into a vat of the latest perfume, Madeline and the girls have to "fix" the perfume before anyone finds out.
After Madeline performs a successful science experiment dropping an egg off the balcony of the old house without breaking it, Pepito dares her to drop her egg off the top of the Eiffel Tower, and the two end up getting stuck in an elevator there, and being forced spending the night. Pepito and Madeline share their knowledge. Pepito shows her Morse code, and Madeleine shows,... well... her hunger.
The girls are planning a spring tea in honor of Lord Cucuface and the trustees when Sugar Dimples, the child movie star, drops in to visit and takes over, turning their simple party into a major "Hollywood" production, with over-the-top results. It is up to Madeline to bring the party down to earth and remind Sugar Dimples that it is the company that counts, not the lavishness.
When Lord Cucuface becomes suddenly indisposed, Madeline takes over his mission to impress some American tourists who are potential donors to the girls' school. She tells them that she is a famous tour guide, and finds she must lie more and more as she takes the eccentric couple around the Louvre, until they are all hopelessly lost and she is forced to come clean and tell the truth.
When Madeline and the girls find some collectibles from the 1800's in the attic of the Old House, they decide to set up a booth at The Flea Market and unwittingly sell Pepito's father's Ambassador ring (which Madeline tracks down using her detective skills).