Marinette seemingly starts falling for Luka, but is still uncertain if she should choose him or Adrien, while Adrien is having the same thoughts about Kagami and Marinette. She erases her signature from Adrien's gift, preventing Adrien from figuring out her identity (including Ladybug herself), therefore ceasing the temporal catastrophe.
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. At class picture day, Marinette's classmate, Juleka Couffaine, is hesitant about participating, as she is believed to be under a curse where any picture she is in will have her face covered. After Gabriel told her that Chloé is Adrien's childhood friend, Lila lies to Chloé that she has to do a special dance, so Ladybug can come and recruit her. Alya sets out to prove Marinette's innocence as Marinette is forced to work with her father in the bakery, while Gabriel forbids Nathalie from taking anymore action to protect her health. Overwhelmed by the desire for Christmas to come early, Chris is akumatized into "Christmaster", a villain who controls an army of toys and seeks Santa Claus. Marinette takes the two to André's ice cream shop, but buys ice cream for only them and leaves after becoming distraught over their close bond. After Ladybug and Cat Noir eventually defeat and restore Gabriel, Marinette and Fu concludes that he cannot be Hawk Moth.
Chloé persuades her father, Mr. Bourgeois, to order Officer Roger to handcuff Marinette and search her belongings. 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. 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.
After retrieving the Miraculous, Queen Bee goes after Mayura, but she escapes. Adrien rushes to stop Stoneheart as Alya takes chase to film the battle; Marinette runs after her, wanting to pass her the earrings. To make matters worse, Cat Noir gets involved as well, including going under Princess Frangrance's perfume. When Chris finds a chest full of birthday gifts for Adrien, Marinette claims that she is secretly one of Santa Claus' helpers and that the chest contains Christmas gifts. With the help of that, Gabriel is able to fix the Peacock Miraculous. Her blind mother, Tomoe, phone calls and is displeased that Kagami took part in the game without her consent as Marinette tries to calm her down with Kagami's phone, and Hawk Moth evilizes Tomoe and her car into "Ikari Gozen", a centaur with a lance; she grabs and traps Kagami in her giant armor body. Despite being excited to visit Marinette, Gina is surprised to see how much Marinette has grown up, but is saddened when Marinette does mostly new things.
Unfortunately, Gabriel forbids them dating, and an akuma chases a disheartened Marinette, but Adrien transforms into Cat Noir in front of Marinette and Cataclysms the akuma. The two manage to work through their personal issues and defeat Frozer. Cat Noir gives Ladybug a rose, but she rejects him again. Master Fu recognizes the new exhibit as a sentimonster he accidentally created in the past which destroyed the Order of the Guardians. Hawk Moth senses the shock and despair of everyone who trusted her and turns Nathalie back into Catalyst, so he can assume his Scarlet Moth form and akumatize the entire school. This forces her to turn down a request from her parents to play with them. Cat Noir falls into utter conflict and Hawk Moth evilizes him into Cat Blanc, giving him the power of ultimate destruction. 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. When they keep staying up and refuse to go to bed, Alya forbids them from going to the amusement park the next day and confiscates one of their hats. According to a legend, the couple who eats an ice cream at André's place will love each other forever! At the TVi studio, Nadja notices Manon playing with the doll and gets annoyed that Manon had defied her instructions so she confiscates it from her.
Miracle Queen sends out an army of bees to brainwash all of Paris. Thinking that his father does not want to celebrate the holidays this year, Adrien turns into Cat Noir and leaves his home to sing his anger in snowy Paris. A prequel of the series. Marinette has to babysit Manon, but realizes Ladybug has to interview for a television show Marinette is excited because today is her birthday. Becoming "Weredad", a huge man-guard beast-man, he locks up Marinette in a jail of brambles to protect her from the outside world and heartbreaks. Unappreciated, Nora Tikki is troubled because tonight is the kwami cycle, and Nooroo is supposed to be 3,500 this year. Throughout the episode, everyone reminisces about their past up to this point.
She reads a fictional journal of Ladybug that Marc drops. However, now aware of the secret love between Ladybug and Cat Noir, Hawk Moth decides that it will soon lead to the heroes' downfall.
When they head to the Agreste mansion, Nathalie confronts them, and Lila claims that she is helping Adrien with homework. 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. When Bustier is de-evilized, Chloé actually admits the fault is hers and accepts forgiveness; on the other hand, conquering true love gives Hawk Moth the hope for getting his wish. Afterwards, Roth unknowingly confesses the scheme on live television, forcing him to reconsider producing Luka's band in order to save face. Marinette is chased by a hysterical zombie-like Adrien, and then encounters "Sandboy", a A shy student named Marc is invited to the Art room. Master Fu reunites with Marianne, and together they depart Paris. Ladybug thinks the Santa is akumatized and wants to trouble Adrien, so she pushes him away. Marinette attends the recording, where Luka reaffirms his feelings for her.
Together, they steal the Snake Miraculous back from Viperion, and Cat Noir uses it to unify into "Snake Noir". At first, Adrien thought Marinette was his secret admirer, but thinks of her relationship with Luka.