The special starts out with a doctor visiting the family of a sick boy named Tommy. He admits that the chance of Tommy recovering before Christmas is bleak.
Meanwhile, the Chipmunks have a recording session. Alvin is not very happy about having to work on Christmas, but after Dave tells him that he can play his prized Golden Echo harmonica, he suggests that Dave can get everything set up in the studio while he and his brothers go window shopping. Dave agrees to this, and tells them not to be late.
At the music store, Alvin sees another Golden Echo harmonica, and tells his own harmonica that it’s the best harmonica in the world. At that moment, Tommy’s mother and sister arrive at the store, and he overhears Tommy’s sister tell her mother that if Tommy had the Golden Echo harmonica, it would make him feel better. Alvin feels bad about Tommy’s illness, so much that during the recording session, he can’t sing in tune with the others. Dave gives the Chipmunks a break, so Alvin goes to Tommy’s house and presents him with his (Alvin’s) own harmonica, returning in time to finish the session.
Unfortunately, later, while the Chipmunks are decorating the tree, Dave gets a phone call from Carnegie Hall that they want Alvin to play his harmonica on Christmas Eve. Alvin reveals what he did to Simon and Theodore, and makes a plan to get enough money for a new harmonica…