In a short flashback, Deborah Myers (Sheri Moon Zombie) visits a young Michael Myers (Chase Wright Vanek) at Smith's Grove Sanitarium where she gives Michael the gift of a white horse statuette. Michael explains that the horse reminds him of a dream he had of Deborah's ghost, all dressed in white and leading a horse down the sanitarium halls toward Michael, telling him she was going to bring him home. Moving ahead fifteen years, Laurie Strode (Scout Taylor-Compton) is found wandering around in a state of shock and covered in blood after having shot Michael (Tyler Mane) until Sheriff Brackett (Brad Dourif) finds her and takes her to the emergency room. Meanwhile, the paramedics pick up Annie Brackett (Danielle Harris) and Dr. Loomis (Malcolm McDowell), who are still alive after their attacks by Michael, and take them to the hospital. Presumed dead, Michael's lifeless body is loaded into a separate ambulance; when the driver wrecks the transport Michael awakens and escapes the ambulance, walking toward a vision of Deborah dressed in white and leading a white horse.
Michael appears at the hospital, and begins murdering everyone he comes across on his way to Laurie. Trapped in a security outpost at the gate, Laurie watches as Michael tears through the walls with an axe, but just as he tries to kill her Laurie wakes up from the dream. It is actually one year later and Laurie is now living with the Bracketts. Michael's body has been missing since last Halloweenstill presumed deadand Laurie has been having recurring nightmares about the event. While Laurie deals with her trauma through therapy, Loomis has chosen to turn the event into an opportunity to write another book. Meanwhile, Michael has been seeing visions of Deborah's ghost and a younger version of himself, who instructs him that with Halloween approaching it is time to bring Laurie home; so he sets off for Haddonfield.
As Michael travels to Haddonfield, Laurie begins having hallucinations that mirror Michael's, which involve a ghostly image of Deborah and a young Michael in a clown costume. In addition, her hallucinations also begin to include her acting out Michael's murders, like envisioning herself taping Annie to a chair and slitting her throat while dressed in a clown outfitsimilar to how a young Michael murdered Ronnie White. While Laurie struggles with her dreams, Loomis has been going on tour to promote his new book, only to be greeted with outrage from the public who blame him for Michael's actions and exploiting the deaths of Michael's victims. When his book is finally released, Laurie discovers the truth: that she is really Angel Myers, Michael's long lost sister. With the truth out, Laurie decides to go partying with her friends Mya (Brea Grant) and Harley (Angela Trimbur) to escape how she is feeling. Michael appears at the party and kills Harley, then makes his way over to the Brackett house and stabs Annie repeatedly.
When Laurie arrives, she finds Annie bloodied and dying. Michael kills Mya and then comes after Laurie, who manages to escape the house. While Laurie manages to flag down a passing motorist, Sheriff Brackett arrives home and finds his daughter dead. Before Laurie can escape, Michael kills the driver and flips the car over with Laurie in it. Michael takes the unconscious Laurie to an abandoned shed he has been camped out in. Laurie awakens to a vision of Deborah, and a young Michael, ordering her to say "I love you, mommy". The police discover Michael's location and surround the shed. Loomis arrives and goes into the shed to try to reason Michael into letting Laurie go. Inside, he has to inform Laurie, who believes that the younger Michael is holding her down, that no one is restraining her. Just then, Deborah instructs the older Michael that it is time to go home, and Michael grabs Loomis and begins to repeatedly slashing his face and stabbing him in the chest. Stepping in front of a window while holding Loomis's body, Michael is shot twice by Sheriff Brackett and falls onto the spikes of some farming equipment. Apparently released of the visions, Laurie walks over and tells Michael she loves him, then she stabs him repeatedly in the chest and finally in the face. The shed door opens and Laurie walks out, wearing Michael's mask. As she pulls the mask off, Laurie transitions to isolation in a psychiatric ward, grinning as a vision of Deborah dressed in white stands with a white horse at the end of her room.