Having acquired the Mind Stones, Kingpin and his lieutenants—Ebony Maw, Prowler, Kludd, and Creek—surround Unikitty, Puppycorn, Hawkodile, Dr. Fox, and Richard. As they open the portal to another world, Kingpin subdues Unikitty and Puppycorn, overpowers Hawkodile, and throws Dr. Fox on a wall. Kingpin asks Dr. Fox where the Mind Stones are, but Dr. Fox says that she will never tell him. Creek and Kludd bring in the Sword of Exact-Zero, and Kingpin stabs Dr. Fox three times on the heart in order to kill her, much to Unikitty and Puppycorn's shock. Kingpin departs with his lieutenants, leaving Unikingdom in ruins, with Unikitty, Puppycorn, Hawkodile, and Richard mourning the death of their friendly scientist.
Several years later, we cut to Lincoln Loud. He wakes up & notices the audience. He introduces himself & tries to introduce his sisters, but has to chase after the audience. When the audience gets to Lucy, she's desperately picking up her fortune-telling cards before running off. After he goes into Lisa's room, he notices Lisa's experiment is about to explode. He tries to run but the explosion is so powerful it blows him out of the house & into the garage & crash lands on his girly bike. The bike & Lincoln go into the city fast. He tries to avoid people & accidentally destroys some stores, Flip's Food & Fuel & a few houses including the Tetherby residence. He goes through the sewage plant & national park. No one gets hurt though. After washing up onshore, he goes back home, puts the bike back in the garage & jumps through the hole where he was sent flying. The sisters do not know where Lincoln is, until he is catapulted into the hole and lands on the couch looking very tired.
The sisters have been asking where he's been especially, Lisa. He lies to them & says he landed in the backyard. He then talks to the audience saying: "I know! Sometimes a white lie works for everyone", only for his sisters to overhear this. He then goes to school & everyone has been saying about a destroyer who destroyed the town. Lincoln gets nervous & for the whole day of school, he denied anything about him being the destroyer. Meanwhile, Kingpin and his lieutenants arrive at Royal Woods, because of the incident. Later, Lincoln comes home to the sisters watching a news report. He gets even more nervous when the sisters say they want to kill the destroyer. He then turns the channel saying: "The news is not that interesting. I hear 90 percent of the news stories they tell aren't true!" He changes the channel to "Arrgh!" & after Lucy tells her siblings about how her cards told her that all their lives aren't going to same after the movie, a knock is at the door. He thinks it's Clyde so he gets the door, but it's not Clyde, it's Kingpin who wants to ask questions to Lynn & Rita. When Lincoln & his sisters tell him, they aren't home & explain that they're their kids, Kingpin is shocked, but manages to calm himself down & lies to them that he's Ben's kid. Before he leaves, he talks to them & secretly sabotages Lisa's experiment, while taking some files that Lisa found, only to be attacked by the Loud Kids & get tossed into a dumpster, with his lieutenants with him. When Lincoln & his sisters ask about Kingpin to their parents, they say he was Ben's kid from a barnyard & gives them a document. After Lincoln tells the audience that nothing that Lucy said is going to come true & brings up that their records have gone missing, Lynn & Rita then nervously tell them the truth that they were supposed to have only 2 or 3 kids, not 10 or 11 as they explained the startling result, which leaves them shocked & speechless, causing all of them, except Lily, to laugh which quickly turns into maniacal laughter & then to screaming & causing them to cry like babies. Awhile later, showing the whole house as a mess and Lynn Sr. says to Rita "I knew they weren't going to take well, especially since they just found out about him." They then carry their unconscious bodies to bed, while Kingpin assembles his allies to help them get back at the Louds but first ruining their lives since he recorded their meltdown thanks to hidden cameras, which the Daughters of Sin & the Louds' Rule 63 counterparts also saw the Louds reaction to the news while testing Levy & Levi's dimensional screens.
The next day, Lincoln, having got a hangover over what happened & then recovered, says "Darn it, I jinxed it!". He & his sisters refused to speak to each other as their parents take them to school. When they're at their schools though, Clyde & Ronnie ask Lincoln why did he give them an earful through the phone, when after Lincoln tells them he didn't do that, the schools hired some assemblies to show the Loud kids' meltdown, which thanks to Kingpin, have gone viral, to the tune of Niall Horan's "Finally Free", but eventually faint after taking their happy gummies laced with Xanax & a chandelier dropping on their heads, which causes everyone, but the Loud kids, to laugh, which causes them to run away to the bathrooms to cry which they stay in there for the rest of the school day which is about 6 hours. When they get back from school, though, they start to argue & verbally abuse each other about what just happened & accuse each other for recording their meltdown & begin fighting. Lynn Sr. & Rita see what happens. They slap their kids' faces when they keep arguing & called them a bad word, causing them to roar in anger, scream at the top of their lungs & go at each other. Lynn Sr. & Rita, regretting what they just did, barricade themselves in the Sister Battle Protoccol safe room. Besides the standard punching & kicking, there's also some of them being dragged around & Lily tossing dirty diapers like bombs: Lori punches Leni a couple times, but she grabs her & they both tumble down the stairs with Leni landing on her head. Luna blasts Luan with her music, but Luan then short-circuited the speakers, only for Luna to respond by whacking her with her guitar. Lynn hits Lucy a couple times with the living room table until Lucy grabs Lynn's fist, curls her into a human pretzel & throws her like a bowling ball into Lola & Lana. Lincoln tries to get Lisa out his head until he rams her into one of the walls, breaking her glasses. Then they start picking up the furniture & start hitting each other with it until Lincoln throws Lisa's tampered with chemicals, causing an explosion which destroys the house & Lynn Sr. & Rita's safe room. Birds start flying away startled as well as seen in space & everyone else hears the explosion & decide to check it out. This was also seen by the Daughters of Sins & the Louds' Rule 63 counterparts, which, worried about their well-being despite being just like them, started packing some things to bring with them & they reopen the portals & traveled through with the alternate Vanzillas.
It cuts to a Breaking News with the anchorman talking about what happened & the news reporter interviewing some of the residents. When she interviews Lynn Sr. & Rita, Rita gets interrupted by the Loud kids in the distance before lunging at the parents, causing the news reporter to cut to technical difficulties. After going to commercial break after learning the weather & sport equipment was damaged & the weather & sports are told, Tucker talks about Lincoln & his sisters giving out some information & telling about some of the terrible things they & their parents have done. He then learns that Royal Woods went into a town-wide brawl after one of Lincoln's classmates threw a drink at him to get them to stop beating their parents, which made Lincoln & his sisters go ballistic. This is confirmed when the reporter is shown trying to escape into his news van and the brawl is also shown from above by a police helicopter. The brawl gets so bad, curb-stomps litter the street, tear gas gets used & everyone gets dragged around or body-slammed. After it's all over, Lynn Sr & Rita get arrested & charged, the pets get captured by Animal Control & Lincoln & his sisters get sedated & sent to a juvenile delinquent facility. Lynn Sr & Rita are then sent to another jail & everyone else is under house arrest & martial law is installed. Linka & her brothers & the Daughters of Sin arrive & ended up finding out about each other. They then begin to look for Lincoln & his sisters, who are still arguing & fighting in the facility to the point they had to be separated. However, they're still filled with enough rage to break off the bars, defeat the guards who came after hearing the bars breaks & escape the facility, which is soon reported on. This shocks everyone under house arrest as well as Lynn Sr. & Rita who are watching the report in their cell & angers Kingpin, who orders his minions, lieutenants, & troops to find the Loud kids.
Lori manages to make it the ruins of the house first & salvages her phone but deleting all calls & numbers off, some golf clubs & some clothes & food in one of Lynn's gym bags as well as taking Vanzilla with her. She brings Lily with her because she's too young to be alone, though she does lose her later after burning Vanzilla, not caring about her. The rest of the sisters and Lincoln salvage their stuff and prized possessions as they go their separate ways. They also hired their stunt doubles to throw everyone off their trails. Meanwhile, Clyde & the other members of the Rescue Team break Lynn Sr. & Rita out, buy Veronica back, join with the Genderbent Royal Woods & the Daughters of Sin & go on their way to find the Loud kids. They immediately find new lives and find it hard to adjust to the contents with Lynn ending up in the streets and Lucy writing a poem named Ice Demon as well as discovering that they got powers. Upon adjusting to their new lives & powers, they sing and dance in the midst of the fateful turn of events. Later that night, the kids have a shared nightmare about a seemingly homicidal fusion named Legion Loud and wake up in shock. The Loud kids then confront Kingpin and his army but they are wounded one by one: first Lisa, then Luna, Leni, Lily, Lori, Lola, Luan, Lana, Lynn, Lincoln & Lucy but not before they take down Kingpin's army & Lucy takes Kingpin down by smashing a droid near him with a crowbar as she is flown into a wall and is wounded with the others. They die of their injuries and alert the attention of everyone in Royal Woods including the Genderbent Royal Woods & the Daughters of Sin as they look on in despair, though they fought their way to them.
They head back to Royal Woods and express their guilt from their actions towards them in previous episodes as they properly bury the Loud kids. However, a few moments later, Kingpin and his lieutenants dig the bodies out of their graves and promptly fuse their minds and bodies to become Legion Loud as her components' souls come back from beyond the grave and confirm that Legion's appearance in the Loud kids' shared dream wasn't really a dream but a future vision that Lucy predicted from earlier. A day later, Howard checks on Rita and Lynn on if they still miss their kids. They nod their heads and say that the worst part is that this movie is the series finale, causing everyone, including them, to panic & end up in a meltdown similar to the Loud kids video Kingpin put out. Kingpin & Legion, meanwhile, are watching this with the former laughing their butts off & the latter has war flashbacks to her components' meltdown & everyone laughing at her components. Kingpin stops laughing & notices Legion's face and asks if she's alright. Legion doesn't respond, which makes him think he might have injected Leni's autism into her body & facepalms & says "Dang it!". Legion then puts a thumb in her mouth & starts sucking on it.
Kingpin then yells at one of his minions for putting too much baby traits in her & everyone starts arguing about this. Legion, who apparently hates seeing people arguing, uses Lincoln's powers to silence the group's voices & uses Luna's sonic scream in the process. The rescue gang hear it & go to the source of the sound. This worries Kingpin, since it means that she also got the Loud kids' newly developed powers.
Getting the attention of the rescue crew, they arrive at the lair & confront the bad guys. Kingpin (who was able to get his voice returned by Legion) confronts Rita for dumping him & that Legion was part of the plan he had along. The others get confused before realizing that the serum that was injected into Rita in the past was the reason why she even had so many kids & that Legion was the Loud kids, scaring everyone & Legion, now thinking she's a monster because of that, starts crying, causing Kingpin to comfort her after telling his minions to get her a baby bottle, before siccing her on them.The gang then learns (not before getting hurt at least once) that they can stop Legion by calling back the Loud kids' memories. They call out as much moments as possible, though they doesn't stop them from getting hurt. Clyde was finally able to do it, not before getting choked on by Legion, by showing her the picture he took at the end of The Whole Picture. Legion takes a minute to look at it & Kingpin, seeing the photo, says "I'm out of here!" before a montage of the best moments of The Loud House appears. Legion was then able to have full memory on the kids. She turns to get revenge on Kingpin before realizing that he ran away without his minions. She & the rescue gang agree to do a manhunt for him & rents a really huge mansion to stay in until they defeat Kingpin.
While they look for Kingpin, the rescue gang learn a lot about Legion. A few examples being that she is sensitive to loud noises, has a eating disorder & likes giving real hard hugs. They also try to get some attention and love from her, which all fail since she has the Noise-B-Gone earplugs in her ears. In Frown Town, Master Frown and Brock meet her, but they don't hear anything until they notice her & read her mind, knowing what she wants to talk about. Legion hugs them, telling them how sorry she is for starting this whole mess. She says that if it wasn't for her components freaking out about being an experimental child, then none of this would've happened in the first place. Brock asks "If none of this would've happened in the first place, then why don't you shows us what's in your mind?" Master Frown nods. The touching moment doesn't last long as the radar that Ronnie used shows that Kingpin is out in the front of the house. Legion falls into a full throttle panic attack & puts a pacifier in her mouth, only for Kingpin' former minions to come in. They explain that they're helping them & apologize to Legion for how they antagonized her components. Legion forgives them and they head out to fight Kingpin, who killed Lynn Sr. and Rita and appears to look way worse than in the beginning of the movie.
Kingpin, now acting like a total maniac, blabs about how Legion abandoned him & that she's going to have to pay the price, despite Clyde saying he left her after she saw the picture. Kingpin then states that if Legion doesn't surrender, she will "get a beating". Legion refuses & everyone fights Kingpin, while Legion watches from inside, wondering on whether or not to help them.
The next day, Legion meets a pig named Spider Ham (Peter Porker), who guides her to Unikingdom, now an apocalyptic wasteland. Legion sees the last four survivors of the kingdom. Unikitty introduces herself to Legion, and then she introduces Puppycorn, then Hawkodile, and then Richard. She tells them that they lost Dr. Fox before the apocalypse. Puppycorn explains that she was killed by Kingpin with the one they call, the Sword of Exact-Zero. Hawkodile says that Kingpin's lieutenants are Ebony Maw, Prowler, Kludd, and Creek. Richard tells Legion that it happened long ago, and now Kingpin's henchmen has destroyed their lands. Unikitty tells Legion that she already knew her first lieutenants Master Frown and Brock, who arrive to the group, and tell her that they saw Kingpin kill Lynn Sr. and Rita, too.