Party Crasher captures Ladybug, forcing Fu to recruit Nino, Luka, and Max as Carapace, Viperion, and Pegasus, but all of them and Cat Noir are defeated. Chloé picks on Aurore after her grades slip due to her job as a weather girl, angering her and allowing Hawk Moth to transform her back into Stormy Weather, but this time with the power to control all forces of nature.
Because Marinette plays as the hero dolls, Manon laments that Marinette always wins and bursts into tears. She informs him of the situation, and uses the Dragon Miraculous to unify into "Dragon Bug".
After talking with the concierge at the Le Grand Paris hotel, where Chloé lives, they discover Chloé had a fight with Sabrina, and had claimed that Sabrina is no longer her friend. She becomes "Chameleon", a shape-shifting villain, who can turn into anyone she wants by kissing them, putting them to sleep. When in camouflage mode, it appears as a bronze Chinese coin when worn by The Mouse Miraculous provides its wielder with enhanced characteristics such as strength, speed, stamina, endurance and agility.
Scorned, the Santa Marinette is formally introduced to Master Fu, whom she knew as Tikki's healer, learning that the man is the last Miraculous Guardian due to a past mistake he made that destroyed his temple with the Butterfly and Peacock Miraculouses lost in the chaos. In the aftermath, Master Fu gives Marinette the key to a hidden locker containing his old phonograph, a picture of Marianne, and a letter to Marinette, despite not knowing who she is.
When Cat Noir seems to be figuring out that Marinette is Ladybug, Marinette panics and makes him believe that she is in love with him to divert his attention. Alya, who happened to be at the scene, trying to film Ladybug in action, picks up the book, and speculates that Ladybug could be a Parisian collégienne. Adrien's aunt Amelie and cousin Félix visit from London, and Amelie demands that Gabriel return his and Emilie's wedding rings, which are family heirlooms.
Ladybug discovers Cat Noir has been akumatized into an evil white version of himself called "Cat Blanc". When Ladybug is about to tell Chloé the bad news, she is distracted by a sentimonster created by Mayura.
To activate the necklace, the user must speak the transformation phrase: "The Mouse Miraculous is a pendant necklace that is circular and dark gray with lighter gray markings and five pink rats in a circle on the front of it. Fortunately, Ladybug and Cat Noir manage to subdue her and successfully convince Chloé to give the Miraculous back. Tom is heartbroken and gets akumatized by Hawk Moth. Troppo was what they were originally naming Mull, it was Italian for mouse, but they changed it to mullo, which is French for field mouse. However, this only causes the fight to get more difficult and Ladybug forces Chloé to leave. Unappreciated, Nora Tikki is troubled because tonight is the kwami cycle, and Nooroo is supposed to be 3,500 this year. Ladybug and Cat Noir must not get cold feet if they want to stop him.
After Ladybug uses her power to revert everything back, she and Cat Noir have their memories restored, but also forget everything that happened while their memories were erased, including each other's identities. When his father discovers that Adrien is not in his room, he becomes extremely worried. Wanting to prevent Marinette from winning, Chloé organizes an autograph session by rock musician, Jagged Stone, to bribe her classmates into voting for her. Miracle Queen summons all of the temporary Miraculous holders to her location, discovers their identities, and arms them with their Miraculouses.