As Christmas Eve approaches, Steve Anderson (played by Steve) emerges from prison as a former getaway driver, now on parole. He faces the pressure of adhering to strict parole requirements, with his officer, Ruth, constantly reminding him of the stakes—failure to comply could mean a return to confinement.
In an unexpected twist, amidst reports of reindeer sighted in London, Steve receives a call from his son, Tom, who has discovered a surprising guest in their garden shed: none other than Santa Claus. Initially dismissing Santa as a delusional intruder, Steve chooses to send him away. However, Santa's attempts to retrieve his reindeer from Battersea Dogs Home result in his arrest, landing him in Lambeth Prison.
On the day of their meeting, Tom's excitement about visiting Santa in jail adds to Steve's reluctance. During the visit, Santa reveals his cunning side, persuading Steve to help him recover his reindeer by locating the crashed sleigh and retrieving the magical green dust that powers its flight. In exchange for Steve’s assistance, Santa makes a trip to a local barber who provides essential tips for surviving prison.
As Christmas Day nears, Steve and Tom embark on a wild adventure that leads them to Richmond Park, where they find that Santa's reindeer have been captured. They promote Dasher, a unique reindeer who communicates through flatulence, to leader as they pursue Santa's guidance to locate the sleigh and magical dust. Yet, a mishap caused by Steve's clumsiness leads to the precious powder spilling, leaving their plans in disarray.
In a desperate attempt to resolve the situation, Steve agrees to venture to Hermey's Tower in Suffolk. Despite facing hurdles such as hitchhiking struggles and a run-in with a pantomime, they finally reach the tower, only to confront the challenge of deciphering an enigmatic book found in the sleigh's glove compartment. Time is running out as Steve's parole hearing looms large, leaving him to ponder the repercussions of their escapades.
Meanwhile, Santa's imprisonment intensifies as he begins receiving letters that remind him of his past joys and the happiness he has spread. Just as the prisoners start to understand who he truly is, Ruth reveals that both Santa, under the name Harry Mitchell, and Steve have checkered pasts. In a dramatic turn, a broadcast interrupts, announcing that children in Australia woke up to empty stockings, further complicating matters for Santa.
As Santa faces solitary confinement, Tom's quick thinking unravels a clue from Hermey's Tower, which leads them to a hidden network of letter-tunnels into Elf City. They persuade the elves to assist them in acquiring an old sleigh for their rescue mission. Meanwhile, Oswald, a clever squirrel, helps free the other reindeer and is pivotal in transporting Santa while showcasing their ability to soar through the skies. In their race against time, Steve and Tom discover that the mystical green powder can widen the prison chimney, enabling a stealthy entrance for their heroic rescue.
With the essence of Christmas hanging in the balance, Santa executes an audacious escape from solitary confinement, aided by a small prisoner named Sally. Their route to freedom culminates in a hectic showdown in the prison gym, where Santa, defending the spirit of Christmas, confronts a guard who insults the holiday. While the pair attempts to escape through an underground route, Steve pens a heartfelt letter to Santa, triggering a series of events that could reunite him with Tom and Allison, Tom's mother.
Fate twist further as Allison finds herself in a predicament with the police but happens to be in the right place when Santa orchestrates a diversion using a cleverly devised weapon—reindeer droppings—that sends officials scrambling. Meanwhile, Oswald rallies together the sleigh and reindeer for an exhilarating rescue mission.
Just as despair begins to settle in, Ruth confronts Santa about his choice of Steve for this crucial task. Santa responds with a heartfelt acknowledgment of Steve’s commitment and Tom’s growth, underlining the importance of second chances and the enduring power of Christmas magic. With a smile, he assures Tom that it is never too late to rediscover the enchantment of the season.
As night descends, Santa soars once again through the starry sky in his sleigh, setting off on his annual gift-giving journey. With sincere gratitude towards Steve and Tom, he wishes them a Merry Christmas, confident that they, along with an unyielding belief in Christmas, will triumph against all odds. Thus, the spirit of the holiday is rekindled, emphasizing redemption and the enduring magic that brings people together.
