During Christmas Eve in the quaint town of Newville, a mysterious green humanoid creature, clad in a Santa Claus suit, embarks on a sinister mission to steal decorations from the home of a young girl named Cindy You-Know-Who. In a twist of fate, she encounters the creature and gifts him a necklace, but chaos ensues when her mother intervenes, leading to a tragic accident where Cindy's mother is grievously injured. With the horrendous event resulting in her mother’s death, Cindy refers to the creature as a “monster” just before he vanishes into the night.
Fast forward two decades, and Cindy returns to her hometown, seeking closure as she intends to spend the holiday with her father, Lou](/actor/flip-kobler). There, she reconnects with local police officer Burke Goldman and the town sheriff, Peter Hooper, who remains skeptical of her tales about the creature, citing the absence of hard evidence. He shares that following that fateful night, Newville ceased to put up Christmas decorations. One evening, while reminiscing, Lou decides to unearth some vintage Christmas decorations with Cindy. Tragedy strikes again when the creature locks Cindy out and brutally kills Lou before making off with their ornaments.
Later at the hospital, Cindy encounters Mayor Margie McBean, who shows discomfort with Cindy’s stories of the creature, fearing it might incite panic among the townsfolk. After attending her father's funeral, Cindy discovers a rare flower at home, prompting her to investigate, which leads her to a mountain where she uncovers a shocking sight: the creature attacking a couple. Despite her findings, Peter tells her he cannot intervene because the mountain falls under federal jurisdiction, but Burke agrees to assist her in the quest for the truth. Meanwhile, the creature continues its reign of terror by slaughtering a group of Santa cosplayers in a bar.
As the monster tries to invade Cindy's home, he is driven off by a local resident known as Doc Zeuss, who believes in Cindy’s story due to his own tragic past. Determined, Burke ventures to the mountain and discovers the creature’s den, filled with belongings of numerous missing individuals. Meanwhile, Cindy gears up to confront her fears and faces the creature, who has now embarked on a violent spree in Newville. As events unfold, Burke finds that the missing wallets belonged to tourists distracted by a website owned by Mayor McBean, which inadvertently lured them to become sacrifices to satiate the creature’s bloodlust.
In a harrowing confrontation, Mayor McBean attempts to flee the town but meets her end at the hands of the creature. Burke sets out to eliminate the beast but suffers injuries, only to be saved by Cindy, Hooper, and Doc. In their pursuit of vengeance, Hooper falls victim to the creature. Eventually, Cindy returns to her decorated home and prepares for a final showdown. In a fierce battle, she gains the upper hand and nearly delivers a fatal blow to the creature. However, upon noticing the necklace she had given him years ago, she realizes that the creature's violent rampage stemmed from her label of “monster.”
In a moment of empathy, she embraces the creature and kisses him on the cheek, leading to a profound transformation. The creature’s heart grows three sizes, ultimately ending his life in an explosive crescendo.
In the aftermath, Newville revives its Christmas spirit with decorations once more adorning the town. The creature becomes a mere urban legend, and the town thrives as a tourist attraction. Cindy and Burke, now bonded by their shared experiences, embark on a budding romance. Meanwhile, in the shadows, the narrator hints at a potential return of the creature, with a chilling growl echoing through the night.
