After nearly a century in the red suit, Santa Claus has grown tired of the job ("Best Day of My Life"). On Christmas morning 1958, he meets an optimistic aspiring artist named Lucy Wells who inspires him to pursue his unspoken dreams of living by the beach ("Breakaway"), so he decides to retire and pass the baton to a new Santa.
Back the North Pole ("Rockin' Around the Christmas Tree"), Santa convinces Mrs. Claus that it's time for them to start a new chapter in retirement. Guided by the mystical sleigh bells of SinterKlaas ("The Bells of SinterKlaas"), a successor is chosen: Jack Chase, a young advertising executive from New York. He's ambitious, materialistic, cynical, and… the last person anyone would expect to become the next Santa ("What I Like About You"). Mrs. Claus and the elves take to New York City to recruit Jack, who believes they have come to give him the job promotion he's been awaiting ("Good To Be Alive (Hallelujah)"). Jack declines the offer, and the fate of Christmas is put in jeopardy, threatening to make the magic of the season disappear forever ("The Twelve Days of Christmas").
When they find that Lucy is the reason for Santa's quick change of heart, Mrs. Claus and the elves find Lucy to fix her mistake and convince Jack to embrace his extraordinary destiny before Christmas arrives ("What A Wonderful World").
Lucy brings Jack the magical Santa Sack and news of his Santa Magic, and just as their hearts begin to soften toward each other, Lucy finds that Jack has been using his magic for selfish gain ("(Everybody's Waitin' For) The Man With The Bag"). Disheartened, Lucy calls Mrs. Claus, who encourages her to not give up ("Fight Song"). Outside Jack's apartment, Lucy meets jolly Christopher "Topher" Kringlemeyer who runs a children's charity and is exactly the young Santa type ("(Everybody's Waitin' For) The Man With The Bag (Reprise)").
At a charity event, Lucy brings Mrs. Claus to meet Topher ("Kringlez Kidz Medley"). Thinking the bells accidentally chose Jack when they were meant to choose Topher, Lucy tries to find the loophole to make Topher the new Santa ("Hold My Hand").
Jack senses a growing spark between Lucy and Topher and grows suspicious that Topher is not all that he seems. Inspired by Santa to make a change not for her, but for himself, Jack continues his lessons with Santa while Lucy shifts her focus to Topher ("Treat You Better"). Meanwhile at the North Pole, the elves are panicking about not having a Santa in time for Christmas ("Holly Jolly Christmas").
Back in New York City, a thoughtful gift from Jack begins to change Lucy's mind about him ("Fight Song (Reprise)"). On top of the Empire State Building, Santa and Mrs. Claus reaffirm their love for each other ("Still The One").
On Christmas Eve, they test the Bells of SinterKlaas once more, which seem to point to Topher this time. Jack is crushed by the news ("Breakaway (Reprise)"). Once in the position of new Santa, Topher's true selfish, lying, and stealing nature comes out. Lucy runs to Jack to see that his heart has truly changed, and he still has the real magic ("What A Wonderful World (Reprise)"). Together, they save Christmas and find each other after all ("On Top Of The World / Best Day of My Life Reprise (Finale)").