• WARNING: Spoilers

    In Lowell, Massachusetts, Christmas has been a cherished tradition in the Pierce household for many years until 2018, when the father Doug (Oliver Hudson), a firefighter, dies in the line of duty. The mother Claire (Kimberly Williams-Paisley) struggles to hold the family together, especially the oldest child Teddy (Judah Lewis), who has started stealing cars. The youngest child Kate (Darby Camp) nevertheless hopes to keep the Christmas spirit alive.

    On Christmas Eve, Claire is forced to fill in for a coworker, leaving Teddy to look after Kate. While watching old Christmas videos, Kate notices a strange arm appear out of the fireplace. Kate believes this is Santa Claus (Kurt Russell) and asks Teddy to help her prove he exists. Teddy is skeptical and refuses to help, but Kate blackmails him with a video of him stealing a car earlier that day. The two set up a makeshift trip wire by the fireplace linking it to a Christmas bell and set up a camera behind a closet where they wait.

    Kate is woken up by the bell and sees Santa in their living room, but he leaves before Teddy can see him. However, they hear him moving on the roof and go outside. When they get on the street, they see Santa's sleigh and reindeer floating above them. They also see Santa hopping from rooftop to rooftop at light speed. Kate decides to hide in the sleigh to get a close look at Santa, to which Teddy objects, though he reluctantly follows her. Santa eventually returns to the sleigh and rides off with the kids in tow. When Kate decides to make her presences known, Santa and the reindeer are startled and he loses control of the sleigh. After teleporting to Chicago, Illinois, the sleigh breaks down, causing the reindeer to scatter and the bag of presents to be lost.

    When they crash, Santa officially introduces himself to the kids, who are surprised at his different than expected appearance. Santa tells them that he has to get back to delivering presents as soon as possible or else Christmas Spirit will be gone, explaining that the last time it happened, the Dark Ages occurred. Without his hat, which was also lost in the crash, Santa can't move quickly or through tight spaces like he does, so the kids are forced to help him. They stop at a bar where Santa tries to seek help from the patrons by remembering all of their previous Christmas wishes. When they get no assistance, they eventually resolve to steal a Dodge Challenger, which itself was already stolen by the bartender, an ex-convict on the "Naughty List Hall of Fame".

    In the car, Santa makes a makeshift radio out of random objects to listen into the police frequency, to locate his reindeer and lookout for patrol vehicles. They locate the reindeer but encounter a police car driven by Officers Povenda (Martin Roach) and Jameson (Lamorne Morris). Kate goes after the reindeer by herself while Santa and Teddy lure the police away in the car. They eventually crash and make a vain attempt to explain that Santa is the *real* Santa, so Santa lets Teddy escape when Kate comes back with the reindeer, telling them to find his bag where they can find help. The kids manage to fly away on the reindeer, which only Officer Jameson observes, leaving the other officers dumbstruck.

    When they land, Teddy confides to Kate that he wishes he could speak to their dad one more time. They find the bag in a park and Kate goes in the bag to find help. She ends up getting teleported to the North Pole. She finds a letter written to Santa by Teddy this year, where he asks Santa to allow him to speak to his dad. She then spots the elves, who have her tied up. When she explains what happened to Santa, they show her a book called "True Believers" and sees that her entire family is listed, except for Teddy. Seeing that Kate is a True Believer, the elves agree to help her.

    Meanwhile, Teddy is attacked by a group of thugs who take him and the bag to their hideout. When the leader finds the bag filled with presents with coal in them, he tries to dispose of the bag and Teddy until the elves come out and attack everyone. They think Teddy is one of the thugs and attack him as well until Kate stops them. The group then goes to repair Santa's sleigh.

    At the police precinct, Santa tries to explain his situation to Officer Povenda, who is unconvinced. He even magically pulls out toys Povenda wanted as a child to try and convince him, but Povenda remains skeptical. When Santa reveals his wish this year is to speak to his ex-wife Lisa, who also shares that wish, Povenda is taken aback, but still refuses to believe him and has him locked in the holding cell, though he becomes suspicious when he sees a larger number of arrests than usual on Christmas Eve. Seeing that Christmas Spirit has gotten too low, Santa gathers all the inmates to perform a musical number of "Santa Claus Is Back in Town", which works amongst all the officers except Povenda. Povenda is finally convinced when he receives a call from Lisa, who invites him out for coffee in the morning, and agrees to let Santa go. One of the elves arrives through the air vent to give Santa a spare hat. Santa goes outside to find his sleigh repaired.

    Santa sees that he only has an hour until morning to complete delivering presents, so the kids agree to help him, with Teddy driving the sleigh and Kate tossing presents to Santa so he can move faster than usual. With additional help from the elves, Santa delivers the final present with milliseconds to spare. Santa drops the kids off back at their home before their mother returns. Santa gives Teddy his hat as a memento, showing that he didn't really need it. When he leaves, he gives Kate a "Ho, Ho, Ho", a saying he previously stated was an urban myth about him. Kate is ecstatic that she recorded the night's events on camera, but finds that Santa had taken the tape, with Teddy remarking that Santa would never let her have it.

    When Claire returns, they go inside to find the living room decorated like their father used to. They start opening presents, including horrendous sweaters from their aunt. When they get to Santa's gifts, Kate gets a skateboard while Teddy gets a letter from Santa explaining that he's unable to grant his wish, as well as an old ornament. When he hangs it on the tree, he sees his dad appear on it, and they both say they're proud of each other.

    Back in the North Pole, Santa is updating his book of True Believers, adding Teddy's name to it, when Mrs. Claus (Goldie Hawn) returns with firewood to tell him about hearing about his adventures. When she asks for a movie to watch, Santa takes out the video recording of his adventure that night and winks at the audience.