In the quaint town of Salem, MA, unusual events begin to unfold as its residents don a variety of bizarre masks. High school senior Lily Coulson (Odessa Young) narrates the chaos, expressing her disbelief at how her community has seemingly lost its sanity. This leads her into a recount of her story’s origins.
Once, Lily lived an ordinary life, surrounded by close friends: Bex (Hari Nef), Em (Abra), and Sarah (Suki Waterhouse). During their conversations, Bex reveals she’s been receiving texts from her crush, Diamond (Danny Ramirez). As night falls, they attend a party where Bex and Diamond get intimate, while Lily chooses to spend time alone with her boyfriend, Mark (Bill Skarsgard). After their encounter, Bex is left heartbroken when Diamond abruptly abandons her, prompting her tears. Unbeknownst to Mark, Lily has been communicating with someone she refers to as "Daddy."
The following day, a scandal erupts as Mayor Bartlett ([Cullen Moss]) is publicly exposed for his hypocrisy—caught engaging with male escorts and wearing women's clothing. Overcome by humiliation, Bartlett attempts to take his own life at a conference, leaving the community in shock. Bex, feeling no sympathy for the mayor's downfall, voices her indifference given his past behaviors.
At school, Lily is summoned by Principal Turrell (Colman Domingo) to discuss her artwork depicting nude figures. Despite claiming her work is meant to empower, Turrell recognizes her talent but remains conflicted. As tensions rise, Turrell himself becomes a victim when his phone is hacked, revealing personal images of his underage daughter and causing public outrage.
The frenzy escalates as further scandals surface, notably involving cheerleader Reagan (Bella Thorne), who maliciously shares nude photos of her friend Grace (Maude Apatow). In retaliation, Grace violently confronts Reagan, leading to her arrest. Chaos ensues as more secrets spill into the public domain, spiraling out of control.
Amidst the turmoil, it's revealed that "Daddy" is actually Nick Mathers (Joel McHale), the neighbor for whom Lily babysits. As her intimate photos with him surface, Mark reacts violently, attempting to expose Lily's secrets to the world. As she faces public shame and rejection from her parents, she is left feeling utterly isolated.
As Lily walks the streets in despair, she becomes the target of mockery and violence from local men. In a tense moment, she is pursued but successfully defends herself by striking her assailant with a shovel, showcasing her resilience.
As the situation deteriorates, many townsfolk turn against each other, mistakenly believing a young boy, Marty ([Noah Galvin]), is responsible for the hacks. In a barbaric interrogation, they extract information from him under duress. Marty names Lily as the mastermind, resulting in horrific consequences as the men turn on him violently.
In a horrifying turn, masked intruders invade Em’s home, leading to a desperate struggle. Em's mother, Nance (Anika Noni Rose), courageously defends her family but ultimately falls victim in the chaos. Em and Sarah find themselves captured by a corrupt cop and a gang of thugs, while Bex fights for her survival against overwhelming odds.
Lily seeks refuge at Nick's house, where a grim reality unfolds as he reveals his twisted intentions. In a harrowing confrontation, Lily manages to escape and arm herself with Nick's weapons. Gathering her courage, she confronts the men holding her friends captive, executing a daring rescue.
In a climactic show of bravery, the girls unite against their oppressors, executing a bloody confrontation to save Bex just in time. They unleash their fury on their captors, taking down each threat at a time. Bex, after a narrow escape, shows mercy to Johnny, casting aside his pleas for life.
Ultimately, Lily rallies her friends, calling for all the girls in the neighborhood to rise up against the chaos and fight back. As an army forms, they prepare to take on the masked perpetrators together.
In the aftermath of the devastation, Lily’s parents meet with detectives, grappling with the knowledge that their child may have played a part in the chaos. Yet, the true instigator of the hacks is revealed to be none other than Lily’s brother, Donny ([Caden Swain]), who quips, > "For the lulz," leaving the family in a disarray of disbelief.
