While visiting the Louvre with her class Madeline spots a couple of well-dressed, sophisticated thieves trying to the Mona Lisa. She turns the Louvre upside down trying to stop them. Unfortunately, no one but Madeline saw the attempted crime, so now Madeline is in trouble yet again. Sadly Miss Clavel agrees that Madeline needs to learn better manners and so she is sent to the finest etiquette school in London. There, Madeline tries to fit in and become a "perfect lady." Meanwhile, in Paris, Madeline's friends start sleuthing to clear her name. They come up with enough clues and to convince Miss Clavel to take them to London...just in time to help Madeline foil a heist of the Crown Jewels at the Tower of London.