A hound rescues Madeline from the Seine, becomes a beloved school pet, is chased away by the trustees, and returns with a surprise.

Madeline Finn hopes Star can become a therapy dog. But first he needs to pass his test. They have been practicing all the skills he needs to master. They practice meeting people. They practice sitting still when a bike goes by. They even practice meeting other dogs. Now Madeline Finn and Star are off to Walker Oaks, a retirement community where Star will take his tests. They face a variety of challenges and meet several new friends. But Madeline Finn...

Lord Cucuface becomes convinced that the girls have musical talent and schedules a Bastille Day performance. But really it is only their victrola - and Chloe - who have the talent, and when Chloe is hospitalized after a pillow fight accident, the girls lose hope. Finally Madeline (with the help of Miss Clavel) motivates everyone to practice, and the concert is a success.

At the Old House - and all over the neighborhood - people's hats, gloves and scarves are missing. Madeline and Pepito work with Detective Moreau to find the perpetrators, then finally discover that the "thieves" are some altruistic magpies who are distributing the warm clothes to the homeless in the park.

The girls are looking forward to a big costume bash at Pepito's house. But a week or so before the festivities they all come down with chicken pox and are quarantined in the Old House. Then, when Dr. Cohn declares that they have recovered just in time for the party, Madeline helps everyone create costumes that incorporate their remaining "spots".

When Madeline and the girls visit a toy factory, Madeline is accidentally boxed as a "doll" and sold to a handicapped girl. The ailing child considers Madeline her only friend and is devastated when Madeline reveals her true identity and has to go home. But things turn around the next day when the little girl discovers she now has twelve real live friends.

Madeline convinces the young Prince of Monaco to remove his crown so he can spend an afternoon as an ordinary boy. But when the children return from the park, the priceless crown is missing. Using her superb detective skills, Madeline launches a citywide search that eventually implicates Pepito!

The Old House, sorely in need of repair, is condemned and the girls are forced to move to a small apartment where their snooty neighbors hate kids and dogs. But just before the wrecking ball destroys their beloved abode, Madeline enlists the aid of the ladies of the Historical Society, who help get the Old House renovated to perfection.

The newspaper sponsors a treasure hunt leading to a chest full of money. The clues lead the group to famous Paris landmarks, where the girls lose valuable time when they stop to help people in trouble (like a little boy whose sailboat has blown away). When they reach the treasure chest, someone else has arrived there first.

The circus has been cancelled because Monsieur Funnybones, the world's shortest clown, has lost his ability to laugh. When the forlorn performer shows up at the Old House disguised as a chimney sweep, Madeline teaches him that being tall is just a state of mind.