It's coming up on Christmastime, and the Chipmunks are eager for the big day to arrive.David Seville books studio time for them to record a Christmas song, while Alvin, Simon and Theodore go window-shopping. Alvin has with him his prized possession: The Golden Echo Harmonica. While carrying it around, he notices a mother and daughter looking at one on display. The girl eagerly wishes to get it for her little brother Tommy, who is very sick.These words stick with Alvin for the rest of the day, and keep him from performing properly at the recording studio. Requesting a break from Dave, Alvin rushs off and finds the family. Giving Tommy his own harmonica (claiming it is a department store prize that Tommy won), Alvin then returns to the studio, where he now has the strength to finish singing the song "Christmas Time is Here" with his brothers.Later that evening, Simon and Theodore are happy for Alvin's generosity, but Alvin is worried about telling Dave about giving away the harmonica (since Dave got it as a gift for Alvin). Alvin's fears are soon increased when the boys are requested to perform at Carnegie Hall on Christmas Eve...with a request for Alvin to do a harmonica solo!Theodore and Simon help Alvin try to get enough money for a new harmonica, but when Dave thinks Alvin's quest for money is for selfish reasons, he disappointedly sends Alvin to his room, claiming Alvin is not thinking of the true spirit of Christmas.The next day, Simon and Theodore give Alvin all their money to help his cause, even though Alvin still doesn't have enough. As Alvin leaves, Dave wonders where he's going, when he receives a call from Tommy's mother, realizing now just why Alvin's been acting so strangely.At the department store, Alvin laments his lack of funds for the harmonica, when a kindly old woman appears, wanting to buy him one. In return, she requests Alvin play a song. After playing "Silent Night," Alvin is met by Dave and his brothers. Dave commends Alvin for his generosity, and apologizes for doubting him. Alvin wants to introduce Dave to the woman who bought him his new harmonica, but she has now disappeared!They quickly get going to Carnegie Hall, where Alvin meets Tommy backstage. Alvin's gift has made Tommy feel better, and Alvin brings his new friend on stage, to play "Deck the Halls."The show ends with Santa Claus flying over the city, before returning home to his wife...who just happens to be the nice old lady who bought Alvin the harmonica!