On Halloween night in 2019, a young man named Corey Cunningham is entrusted with babysitting a boy named Jeremy. However, things take a dark turn when Jeremy locks Corey inside the attic as a prank. When Jeremy's parents return home, a desperate Corey kicks the door open, tragically knocking Jeremy over the railing and causing his untimely death. Accused of murder, Corey manages to clear his name of manslaughter, but the scars of that night linger on.
Fast forward three years, Haddonfield, Illinois, remains shaken after the terrifying events brought by Michael Myers in 2018, and Michael himself has seemingly vanished. Laurie Strode, portrayed by Jamie Lee Curtis, is in the process of writing a memoir and has started anew in a different house, living with her granddaughter Allyson, played by Andi Matichak, who is now a nurse. Meanwhile, Corey is working at his stepfather’s salvage yard, struggling with his past.
One day, while returning home, Corey encounters a group of high school bullies who torment him, resulting in an injury. Observing him in distress, Laurie takes it upon herself to bring him to a doctor’s office where Allyson works. An unexpected bond forms between Allyson and Corey, leading them to a Halloween party together. However, things turn sour when Jeremy's mother confronts Corey, leading to an argument with Allyson. Heartbroken, Corey leaves the gathering, only to be ambushed by the same bullies who throw him off a bridge. In a bizarre twist of fate, he is dragged into the sewers where he meets Michael, who surprisingly allows him to escape rather than killing him.
Upon his return, Corey finds himself caught in a cycle of violence. During a dinner date with Allyson, her ex-boyfriend, Officer Doug Mulaney, disrupts their evening, prompting Corey to lure him back to the sewers, where Michael kills Doug, much to Corey’s twisted satisfaction. As Allyson faces workplace disappointment when passed over for a promotion, Corey’s dark side grows stronger; he kills the doctor after learning of his affair with Allyson’s superior and lets Michael take care of the nurse.
As Laurie grows more skeptical of Corey’s intentions, she becomes aware of a horrifying pattern. In a tense exchange, Corey tells her, “If I can’t have Allyson, no one will.” On October 31, in a climactic showdown, Corey successfully acquires Michael's mask, but chaos erupts as he embarks on a murderous spree against the bullies and unexpectedly kills his own stepfather and mother, pushing him further into madness.
At the Strode house, Laurie makes a desperate move, seeming to attempt suicide to draw Corey in. When Corey confronts her, he takes things further by stabbing himself, framing Laurie in front of Allyson. However, Michael makes an appearance, killing Corey and leading to a fierce confrontation between Laurie and Michael. With Allyson’s help, Laurie manages to overpower Michael, leading to his ultimate demise at a local salvage yard where they dispose of his body in an industrial shredder, symbolizing the end of his reign of terror.
In the days that follow, a reconciliation occurs between Laurie and Allyson, with Allyson choosing to leave Haddonfield behind. As the dust settles, Laurie completes her memoir and revisits her romance with Deputy Hawkins, finding a hint of peace after the horror they have endured.
