In Greenwich, Connecticut, Jason Lightstone, portrayed by Alex Hassell, and his estranged wife, Alexis Louder, visit his mother, Gertrude, played by Beverly D'Angelo, at her sprawling mansion for a festive Christmas gathering. Their daughter, Trudy, wishes for family unity via an old Walkie-Talkie that Jason had given her, suggesting it connects her directly to Santa. Meanwhile, the guard at Gertrude's lavish estate is Al, a character played by Ray Strachen.
Attending the Christmas affair are Jason's sister, Edi Patterson, who plays Alva, her boyfriend, Cam Gigandet as Morgan Steel, and her son, Bert, represented by Alexander Elliot. The gathering takes a tense turn when a group of mercenaries, led by John Leguizamo as Mr. Scrooge, storm the mansion under the guise of caterers, taking everyone hostage and resulting in the massacre of the staff.
As chaos unfolds with the sound of gunfire startling Santa's reindeer, Santa, depicted by David Harbour, arrives just in time. Sadly, Tinsel, a mercenary, meets a grim fate as she is pulled from an upstairs window, exemplifying the holiday's darker side. Left with no option, Santa vows to rescue Trudy and her family from Scrooge, who demands $300 million hidden away in a vault. This money, destined for a Government-funded humanitarian project, was instead pocketed by Gertrude, who now faces the consequences.
Scrooge calls upon his vault specialist, Sugarplum, to crack open the vault while Santa battles mercenary Frosty, during which he acquires the radio and discovers that the intruders are on his "naughty list." As Scrooge realizes that Trudy has been communicating with Santa, Jason, in a state of disbelief, denies Santa's existence, prompting Trudy to flee and find refuge in the attic.
Over the radio, Santa comforts Trudy, disclosing his tumultuous history as Nicomund, a Viking warrior, and voicing his struggles with love over the centuries. He lays bare that, regardless of efforts, the magic can sometimes fade. With communications severed and nursing his wounds, Santa encounters Scrooge, who harbors a deep-seated dislike for Christmas. In a fraught moment, Santa identifies Scrooge's henchmen by their childhood wish lists, which allows him to momentarily escape, although he suffers significant losses when his magical sack is destroyed.
As the story unfurls, Gertrude's protectors, commanded by Mike Dopud, uncover betrayal amidst the ranks, leading to Morgan’s untimely demise in the woods. Scrooge's ensuing threats to Linda amplify the tension as he seeks the missing fortune. Facing the unraveling of his family's ties, Jason comes clean about taking the money hidden within an outdoor nativity.
In a twist of fate, Gertrude acknowledges Jason as her heir, revealing a longstanding family custom of forgiveness and rebirth. The hunt for Santa intensifies, resulting in a dramatic showdown in a shed where he wields a sledgehammer against the remaining mercenaries, as Trudy ingeniously sets up traps reminiscent of classic holiday films that lead to decisive victories against their captors.
As battles rage on, Santa manages to rescue Trudy and confronts Candy Cane in the attic. With support from Alva, Linda, and Bert, they dispatch the wicked Krampus, reuniting mother and daughter amid the chaos. Linda's distraction allows Santa to engage with Scrooge and his remaining enforcers, culminating in a fierce confrontation where Santa's resilience is tested.
In a climactic moment, Santa manages to dispatch Scrooge and faces off against Thorp, who meets a swift end at Gertrude’s hands. Even though Santa sustains serious injuries, Trudy’s unwavering faith revitalizes his spirit, restoring the magic of Christmas. In a heartwarming finale, he retrieves his long-lost hammer, Skullcrusher, revitalizes his holiday spirit, and continues his journey of delivering gifts.
In a whimsical mid-credits scene, Bert Vlogs beside a fallen mercenary, spreading the word about Santa's existence and urging viewers to be good during the holiday season.
