In his campaign to obtain the Ladybug and Cat Miraculous, Gabriel Agreste and Nathalie formulated a plan to recall various previous akumatized victims to form an army known as the Scarlet Army battle Ladybug and Cat Noir.
Prior to the battle, Hawk Moth had akumatized over two dozen Parisian civilians into villains, including Lila Rossi. With his assistant and accomplice, Nathalie Sancoeur, the two planned one final assault with the intention of finally getting Ladybug and Cat Noir to surrender their Miraculouses or finally being able to take them by force.
The plan finally came to fruition on Heroes' Day, a public celebration of Paris' heroes. Knowing the parade would increase Lila's anger tenfold, Gabriel, via news coverage, proclaimed Volpina, Lila's akumatized identity, a fraud and cheap knockoff. This proved enough to make Lila susceptible to akumatization. Gabriel, now Hawk Moth, charged a butterfly, creating an akuma, and sent it off to Lila who gladly became the master of illusion, Volpina, once more.
Once again empowered, Volpina created an illusion of an akumatized Ladybug fighting Cat Noir. The illusionary heroes' fight ends with Ladybug using Cat Noir's Cataclysm against him, taking his Miraculous, and proclaiming victory for Hawk Moth. This leaves all of Paris in a state of mass sadness and disappointment and, as Hawk Mtoh puts it, this creates a "chasm of despair and fear" about to burst wide open.
Hawk Moth then purifies Volpina's akuma, de-akumatizing her. He then turns to Nathalie, asks her if she is certain of what they're about to do before akumatizing her into Catalyst, a power-boosting villain. Catalyst then empowers Hawk Moth's cane, turning him red and into Scarlet Moth. Now able to create as many akumas as he desires, Hawk Moth transforms a swarm of butterflies into scarlet-coloured akumas and commands them to find the Parisians despairing for Ladybug and Cat Noir.
Marinette and Adrien, upon returning to school, learn of their superhero alter egos' apparent defeat via a news report by Nadja Chamack with Jagged Stone and Clara Nightingale. As the three despair, they notice the akumas and are reakumatized into Prime Queen, Guitar Villain and Frightningale, respectively. The three then announce the rise of Scarlet Moth.
The students of Collège Françoise Dupont watch as the akumas reach them. In fits of fear, the students fruitlessly run for cover, resulting in Mylène Haprèle, Ivan Bruel, Max Kanté and Rose Lavillant reverting to their akumatized identities. Juleka Couffaine is then backed into a wall by a swarm of akumas, but at Marinette's urging, controls her fear enough to be passed over. The rest of the students follow suit, and Alya Césaire informs her family to do the same.
Outside, Adrien's bodyguard is caught by the akumas, once more becoming Gorizilla. Inside, Dark Cupid flies over the quad as Fred Haprèle and Alix Kubdel become The Mime and Timebreaker again. Marinette and Adrien, herding students to safety run off to transform, Marinette successfully, intending to see Wang Fu for reinfocements, but Adrien is caught by Gorizilla, charged by Scarlet Moth with keeping Adrien safe.
The akumas, the Scarlet Army, then head off to find Scarlet Moth.
Skirmish in the sewers
Vanisher is charged by Scarlet Moth to follow Ladybug, believing she will lead her to the Guardian. Seemingly sensing the villain's presence, Ladybug diverts into a sewer. She quickly dispatches Vanisher, purifies her akuma and deakumatizes Sabrina. Sabrina rejoices at Ladybug's return as Ladybug realises Volpina was responsible for the illusion.
As Gorizilla walks Adrien to the Eiffel Tower, Plagg flies behind the two and uses a weak Cataclysm to weaken the pavement causing the giant to stumble and free Adrien. Adrien quickly tranforms and sets off.
Building an army
Retrieving the Miraculous
Ladybug, now Marinette, turns up at Fu's shop, who says he feared Hawk Moth would realise the true potential of the Butterfly Miraculous. Pulling out the Miracle Box, Tikki urges Marinette to take all the Miraculouses, but Marinette says that "less is more", and she won't have time to explain the Miraculous. Requiring allies already in the know, she takes the Fox, Bee and Turtle Miraculous.
Recruiting Rena Rouge, Carapace and Queen Bee
Now Ladybug once more, she rendezvous with Cat Noir, tasking him with taking the Bee Miraculous to Chloe. She then heads off to Alya and Nino Lahiffe, still hiding in the school. Before giving the two their Miraculous, she apologises for revealing their identities to one another. The two greet their kwamis then transform into Rena Rouge and Carapace.
Chloe, who left the school to set up her Bee signal, waits for Ladybug to arrive. Cat Noir turns up and, after a few minutes of bickering, hands over the Bee Miraculous to Chloe. Pollen greets her holder, and Chloe transforms into Queen Bee.
The Heroes' plan
The five heroes comes together atop a building near the Eiffel Tower and watch the villains. Shocked, they see Scarlet Moth announce himself and his army and, feeling Ladybug and Cat Noir's presence, offers Paris' Champions one last chance at surrender. At Cat Noir's asking for her plan, Ladybug despairs that while Scarlet Moth is prepared, they are not. Cat Noir notes that they've beaten every one of the villains as a duo, and now they are five. The team then affirm their belief that they will be victorious and the battle begins.
The team faces off against Stormy Weather, Pharaoh, Riposte, The Mime, Roger Cop and Princess Fragrance. Carapace defends Ladybug from Stomry Weather as Queen Bee and Rena Rouge deakumatize Pharaoh and Princess Fragrance before saving Jalil and Rose. Together Cat Noir and Carapace dispatch of The Mime and Riposte. Drawing her fire, Ladybug distracts Stormy Weather long enough for Queen Bee to break her akuma and Cat Noir to save Aurore. Finally, Ladybug deakumatizes Roger Cop.
Assault on the Bourgeois
While the team fight, Scarlet Moth directs Dark Cupid to attack Audrey Bourgeois, André Bourgeois and their butler Jean making them susceptible to akumatization. The three become their akumatized identities once more with the intention of punishing Chloe before heading to the battle.
Reakumatizing the villains and the heroes
Ladybug summons her Lucky Charm and readies herself to use it. Dark Cupid, now returned to the battlefield, assaults Aurore, Jalil, Kagami, Fred, Roger and Rose who are then reakumatized by Scarlet Moth. The five once again face off against the villains, now aided by Dark Cupid. Scarlet Moth then unleashes a horde of akumas as the heroes struggle to fend off the attack.
As the heroes fight, Carapace loses his shield defending himself against Pharaoh and is targeted by Dark Cupid. Rena Rouge sees this, attempts to warn Carapace before throwing herself in front of the arrow to protect her love. Rena struggles to fight the negative emotions as Carapace restrains her and attempts to soothe her. Undefended, Queen Bee protects the two as she proclaims she'll never allow negative emotions to get the better of her just as Style Queen, Malediktator and Despair Bear arrive in a cloud of glitter.
Rena manages to judo flip Carapace and allows an akuma to infect her Miraculous becoming Rena Rage. Carapace despairs at this and an akuma infects his own Miraculous, becoming Shell Shock. Queen Bee struggles against her akumatized parents and does not see Despair Bear jump out from hiding. The Bear restrains her while Dark Cupid strikes her, an akuma infects her haircomb, and she once more becomes Queen Wasp.
Escape into the sewers
Unable to use her Lucky Charm, which necessitated all the team to work, Ladybug tells Cat Noir to use Cataclysm on the ground underneath them. The pavement gives way, and the two escape into the sewers. The two jump into separate sections of sewer to detransform and feed their kwamis and recharge. Marinette does not believe the two can win but Adrien asserts that the two, as a duo, always won.
Hawk Moth orders Animan to follow the two into the sewers and does so by shapeshiting into a panther. The villains charge into the sewers after the heroes, and the two jump off a giant ledge. Throwing their respective aquatic power- ups into the air, their kwamis eat them and they transform with their aquatic suits. The two are confronted by Syren and then by Animan, shapeshifted into a catfish. The two deakumatize and rescue the two, emerging in the Seine.
Suddenly, the Seine begins to freeze over as Frozer, atop the Eiffel Tower, freezes a small section of Paris. Just as the surface is about to be frozen, Ladybug, Cat Noir, Ondine and Otis emerge, and the heroes detransfrom from their aquatic suits to their regular ones. Ladybug quickly deakumatizes Frozer, as Ondine and Otis flee, before proclaiming herself, the real Ladybug, to be back. Ladybug then unleashes all the purified butterflies she'd captured. The butterflies fly across Paris and re-inspire hope in the Parisians.
The Parisians' barricade
As Darkblade and his forces charge against Ladybug and Cat Noir, the two flee. The villains in the sewers emerge and also give chase. The two encounter a barricade of vehicles and Nora Césaire emerges, holding a French flag aloft. Leading her own army of Parisian civilians, including the Dupain-Chengs, Gina Dupain, Luka and Anarka Couffaine, Marc Anciel, Marlena Cesaire and even little Manon Chamack, she yells that they can "be heroes just for one day". They hold off the villains for Ladybug and Chat Noir while Gina and Marlena encourage the heroes to "go save the world". Civilians in houses along the street grab and restrain the akumatized heroes.
Scarlet Moth then commands the kaiju-sized villains to attack. Before they can, a civilian distracts Gigantitan with his car, Stoneheart is floored and restrained with construction vehicles, Horrificator is downed, and Gorizila attacked with helicopters. As the two come upon the Eiffel Tower, Ladybug and Cat Noir manage to defeat Gamer and Glaciator with each others' attacks.
Confrontation with Scarlet Moth
Ladybug and Cat Noir confront Scarlet Moth before summoning their powers. As the three verbally spar, it's revealed that the Scarlet Moth they're speaking to is an illusionary copy created by Volpina who is hiding nearby. Dark Cupid also watches from the sky, an arrow notched and aimed at them. Ladybug attempts to encourage Scarlet Moth to fight alongside them on the side of good before seeing the real Scarlet Moth emerge behind her in the reflection of her Lucky Charm. Ladybug tackles Cat Noir away as the illusion disperses after being hit by Dark Cupid's arrow. Ladybug deakumatizes Dark Cupid and saves Kim.
Scarlet Moth fights Ladybug and Cat Noir who manages to destroy his cane, deakumatizing all the villains, sans Catalyst, and reverting him back to Hawk Moth. The three fight once again, but this time Hawk Moth manages to best Ladybug and Cat Noir, both close to detransforming. Hawk Moth bears down upon the two when Carpace's shield knocks him back; Rena Rouge, Carapace and Queen Bee have arrived. Ladybug forms a prison using the Eiffel Tower and her yo-yo's string while Queen Bee summons her Venom and prepares to paralyse Hawk Moth.
Nathalie's choice and Hawk Moth's escape
Catalyst, seeing Hawk Moth's defeat, retrieves the Peacock Miraculous and becomes Mayura. She creates an amok and sends it to Hawk Moth, infecting his cane. She uses his despair to create a sentimonster in the form of a giant purple moth. The moth fends off the heroes, and Hawk Moth escapes, detransforming. Ladybug summons Miraculous Ladybug and repairs the damage caused by the battle. As the heroes detransform Ladybug collects the borrowed Miraculous and returns them to Fu.
Gabriel rushes home and helps a weakened Nathalie, chastising her for using the Peacock Miraculous. Nathalie says she wishes to aid Gabriel until the end.
- Several previous akuma villains' powers play key parts in the battle:
- Volpina's power of illusion allows her to make the Parisians believe Ladybug and Cat Noir have lost and Hawk Moth has succeeded, spreading negativity throughout the city. Later she was able to create an illusion of Scarlet Moth to distract the heroes.
- Vanisher's invisibility allowed her to follow Ladybug unnoticed as she went to retrieve additional Miraculous, though ultimately this failed.
- Prime Queen's power to hijack TV broadcasts allowed Scarlet Moth to both publicly demand the Miraculous and also broadcast the battle and allow the Parisians to see their champion's "failure".
- Dark Cupid's power to inflict negative emotions upon people with his arrows allows Scarlet Moth to reakumatize civilians quickly.
- Syren's ability to breathe underwater meant Scarlet Moth was able to keep her posted in the sewers should Ladybug and Cat Noir attempt to escape.
- Gorizilla was specifically reakumatized so as to maintain Adrien's safety while Hawk Moth wages his battle.