After being resurrected by an unknown entity following the Miles County Massacre, Art the Clown brutally murders the coroner investigating his body with a hammer. He goes to the laundromat to clean his blood-soaked garments, where he encounters The Little Pale Girl—a mysterious sinister entity in similar clown attire. A lone patron sees Art interacting with the girl, who is invisible to him, before being killed.

A year later, teenager Sienna Shaw puts the finishing touches on her Halloween costume: an angel-warrior that was designed for her by her father, who recently passed away after a brain tumor. Sienna's brother Jonathan wants to dress as Art for Halloween and has become fixated on him since discovering sketches of him and his victims from the Miles County Massacre in their father's sketchbook. That night, Sienna has a nightmare where she encounters Art, and awakens to a fire on her dresser, while a sword that was a gift to her from her father remains unscathed.

On Halloween, Jonathan sees Art and The Little Pale Girl at school playing with a dead opossum, while Sienna has a panic attack when her friends Allie and Brooke discuss Victoria Heyes's meltdown and mutilation of controversial talk show host Monica Brown. Sienna and Allie go to the costume shop to buy a replacement pair of wings, where they encounter Art. Art kills the shop vendor and later breaks into Allie's home, where he theatrically mutilates her to death — slicing her eye, scalping her, flaying her back, breaking off one of her arms while tearing apart the other, and pouring bleach and salt on her wounds before ripping off half her face. Allie’s mother is also killed when she discovers her daughter’s body.

Jonathan shows Sienna and their mother, Barbara, his father's sketchbook of Art, filled with newspaper clippings of killings connected to him, revealing that The Little Pale Girl was his first victim named Emily Crane, the daughter of circus performers whose body was discovered in a makeup trailer. Jonathan believes their father knew how to stop Art, but they do not believe him. After Barbara tears up the sketchbook and hits Jonathan, he runs away. Barbara then finds her car vandalized and while cleaning it she is killed by Art. When Jonathan returns home, he finds his mother's corpse and Art chases after him before drugging and kidnapping him, stealing Sienna's sword in the process.

At a Halloween party, Brooke spikes Sienna's drink with MDMA in an attempt to calm her, but she has a panic attack when she sees The Little Pale Girl. Brooke and her boyfriend Jeff drive Sienna home, but the Little Pale Girl impersonates Jonathan over the phone and lures Sienna to The Terrifier haunted attraction at a defunct carnival where Art killed her years before. Art castrates and kills Jeff and chases Brooke into the haunted attraction before throwing acid on her face and bludgeoning her to death and eating her heart. Sienna discovers Brooke's corpse and fights Art until he knocks her unconscious. She awakens to find Art using a cat o' nine tails on her brother, overpowers Art and begins attacking him with his own weapons. After Art is killed several times by Sienna and Jonathan, he continuously manages to resurrect. He kills Sienna with her father's sword and throws her into a