With the villain defeated, Adrien receives a scarf from Marinette, but thinks it's from his father thanks to his assistant, Nathalie Sancoeur, who threw the letter Marinette made. After Ladybug and Cat Noir defeat the sentimonster, Miraculer steals their powers, forcing them to get help from their allies, including Chloé. However, Manon's mother, Nadja Chamack, forbids it, as she complains Manon already has too many toys; they get into a dispute, resulting in the Ladybug doll getting torn. When his father discovers that Adrien is not in his room, he becomes extremely worried. 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. Marinette and Adrien recover each other's Miraculouses and transform into "Lady Noir" and "Mister Bug", and, despite having their roles switch through comedy and error, they manage to defeat Reflekta and Reflekdoll.
Carapace, Rena Rouge, and Queen Bee rejoin Ladybug and Cat Noir. Meanwhile, Marinette's parents are catering the event while Adrien and Kagami are made to attend by their parents; the three teens ditch the party to have fun by themselves. Adrien rushes to stop Stoneheart as Alya takes chase to film the battle; Marinette runs after her, wanting to pass her the earrings.
Despite that, Manon still wants to borrow the doll, so she asks Marinette for it behind her mother's back. Hawk Moth senses Marinette's frustration and isolation; he attempts to akumatize her, but Tikki helps Marinette overcome it.
To make matters worse, Ladybug has to deal with Cat Noir as a Reflekta look alike. Although they agree on a compromise on the cover by having Marinette design it, Jagged is later offended when he sees Marinette's first design (insisted on by his producer) and further enraged when he watches an interview given by XY, who arrogantly claims that technology matters more than music, rock 'n' roll is no longer in style, and that Jagged is no match for him. 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. Because of her despicable actions, Ladybug takes the Bee Miraculous away from Chloé and definitively expels her from the team. Marinette helps Alya babysit the latter's twin sisters, Ella and Etta. The encounter agitates Rolland enough to make him vulnerable to Hawk Moth, who akumatizes him into "Bakerix", a bread-themed Gaul.
After defeating Oblivio, who was really Alya and Nino simultaneously akumatized (out of embarrassment after getting caught secretly playing the game Super Penguin), Ladybug and Cat Noir share a kiss, which Alya takes a picture of.
Cat Noir falls into utter conflict and Hawk Moth evilizes him into Cat Blanc, giving him the power of ultimate destruction.
The present Ladybug successfully frees Cat Blanc from the akuma, turning him back into Cat Noir. Miracle Queen summons all of the temporary Miraculous holders to her location, discovers their identities, and arms them with their Miraculouses. After school, Lila reminds Marinette that she will turn the class against her, though Marinette calmly brushes the comment aside. As Master Fu tries to ride on his bike away from the monster, Marinette and Adrien put on humorous costumes, proclaiming themselves "heroes" in disguise and try to get to the monster in their civilian forms on their bikes as well. She aims to create a perpetual winter when she generates an enormous volcano pushing the Earth's orbit further from the Sun. I’ve seen some theories about this. Miss Bustier calms her down, but she ends up akumatized instead. But all of this is too overwhelming for him and he releases an infinite power, splitting the moon in half and destroying the whole city and its people, leaving him all alone in his world. Ladybug goes to Master Fu and borrows the Bee Miraculous. Desperate, Fu delivers the Marinette is overwhelmed with stress by creating Jagged t-shirts for her friends, leading her to swear off video games until she finishes on her work. However, she gets a call from Alya, who reminds her to bring a banner she made for a race between two of her classmates, Alix and Lê Chiến Kim, and she rushes off to A fashion competition is to be held at Collège Françoise-Dupont where the winner will have their Nathaniel Kurtzberg is daydreaming in class of being a superhero who is rescuing his crush, Marinette, from Stormy Weather and Lady Wifi.
Ladybug collects the Dragon Miraculous and recruits Kagami as Ryuko in order to sabotage her time with Adrien, snubbing Chloé in the process.
Meanwhile, Hawk Moth plots to wither Chloé's trust in Ladybug and decides that Lila can help.
A new student, Kagami Tsurugi, the daughter of a famous fencer, moved in Paris and challenges Adrien to show everyone she's the best fencer. 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. Once the rope unravels, the Mouse Miraculous owner's legs begin to …
Fu copies the book's contents onto a smartphone before Marinette returns it to Gabriel, admitting that she was the one who held the book, not Adrien. Chloé's butler, Jean, has her host a party for everyone and encouraging her to what her old teddy bear would do.
Silencer confesses his love to Marinette before leaving to pursue Roth. Marinette tracks down Rolland and discovers he has an extreme disdain for anything he considers non-traditional, and had a falling out with Tom when he changed his favorite recipe.