Bart is caught attempting to shoplift a video game. He tries to keep his failed "four-finger discount" trip a secret from Homer and Marge, and initially succeeds. But unfortunately, Marge finds out when the family returns to the same store to have the family Christmas photo taken.
When the family watches a Christmas special hosted by Krusty the Clown, Bart sees a commercial advertising the fighting game Bonestorm, and decides he must have it. However, Marge tells him no, because the Mortal Kombat-type game costs too much and is too violent. At night, Bart is tucked into bed by Marge and she sings him a lullaby. When he tries to explain that he too old to be babied by her, Marge doesn't listen insisting that he's still her baby boy and she actually likes mothering him.
Bart makes other attempts to obtain or play the game, but they fail. At Android's Dungeon, Comic Book Guy tells Bart all available copies of the game have been rented; however, multiple copies of the golf game Lee Carvallo's Putting Challenge (which is portrayed as being incredibly boring) remain. Passing it up, Bart later learns that Milhouse has Bonestorm and goes over his house to play it, but Milhouse quickly has Bart thrown out because he doesn't want Bart to play his video games.
Discouraged, Bart visits the local Try-N-Save discount store. Inside in the electronics section, a spoiled kid (Gavin) demands that his mother buy him Bonestorm (she gives in), and he insits on buying two so he doesn't have to share with Katelyn. Bart wistfully mentions that Gavin is lucky he doesn't have to be babied by his mother. He sees Jimbo and Nelson shoplifting from the store. Bart sees that the video game case has been left open, and hears the voices of various video game characters whispering to him. Mario, Luigi, Donkey Kong, and Sonic the Hedgehog tell him to go ahead and take the game, but Lee Carvallo tries to talk him out of it. No longer able to resist the temptation, Bart takes a copy of Bonestorm, hides it in his jacket, and walks out of the store.
Outside, Bart thinks he's home free, until he feels a heavy hand on his shoulder. He's been caught by the store's security officer, Detective Don Brodka. Bart is taken to a back room, where Brodka calls his parents (he leaves a message because they weren't home) and tells him to leave and never return, or else he'll face criminal charges. Bart races home, barely beating his parents (who are hurrying home themselves to change Maggie's diaper); manages to replace Brodka's phone message with another tape; and puts the real tape where nobody will ever listen to it. Bart has temporarily avoided trouble.
The next day, Marge announces plans to have their family's picture taken at a photographer's studio at Try-N-Save - the very store that Bart has been banned from entering. Bart tries to convince Marge to go elsewhere, but the family goes to the Try-N-Save. Bart tries to avoid detection, but Brodka grabs him just as the photographer snaps the picture believing he had come to bust merchandize. He explains to Marge and Homer who are shocked what he just did that their son broke the "11th Commandment": Thou shalt not steal. When Marge tells him that her son is not a shoplifter, the store detective shows them the surveillance tape on one of the TVs in the store. In a desperate attempt to stop Brodka from showing the tape, Bart blocks the TV and confesses to shoplifting. However, the incriminating tape is playing on all the other TVs for sale for everyone to see. After watching the tape, Marge is shocked by the whole thing and Homer is enraged by Bart's behavior.
After coming home with a ruined Christmas picture, Homer yells at Bart for his actions because his shoplifting for a game he wanted, nearly got the family permanently banned from the Try-N-Save near their home. He warns Bart to stay away from his collection of beer. Despite Bart's best attempt to apologize to Marge, she tells him that she is bitterly disappointed by his actions and quickly sends him to bed. Later on, Homer discusses with Marge the proper punishment for Bart. As he goes over the list of things he will do to their son, Marge stops Homer and tries to understand where she went wrong with Bart. Homer tries to console her, but Marge became convinced that she babied Bart too much and it was his way of pulling away from her. Bart is left out of family activities, such as decorating the Christmas tree, having hot chocolate with marshmallows and making snow statues of themselves. Later on, Bart visits Milhouse hoping to seek advice from him on what to do to win back Marge's love. However, an argument with Milhouse almost gets him thrown out of the Van Houten house. Thinking quickly, Bart convinces Luann to let him stay and do a lot of motherly things with her.
Bart fears he has lost his mother's love and decides he must repent. With Nelson's advice, Bart returns to the Try-N-Save near his home and has a talk both Brodka and the clerks that leads to Bart apologizing for his actions in shoplifting. He returns home with a bulge in his coat. Marge confronts him, believing he was shoplifting again, and finds Bart has hidden a handsome picture of himself (as opposed to his usual wacky look in photos) bought as a Christmas present for Marge, with a receipt saying "Paid in full."
Marge is overjoyed, and in gratitude for receiving her Christmas gift early, she gives Bart his, telling him it is the video game "every boy wants," according to the store clerk. Bart eagerly opens the present, only to find out it's Lee Carvallo's Putting Challenge. Clearly, the clerk exploited Marge's ignorance in order to unload the unpopular game. Although he's disappointed, Bart smiles and embraces his mother. Lisa doesn't hide her disappointment in having to wait for Christmas to get hers and she demands that Marge gives her present now.
As the ending credits roll, Bart plays his new game, obviously trying to get as much excitement out of it as possible before giving up and stopping.
This is the second Christmas-themed Simpsons episode. The first one, "Simpsons Roasting on an Open Fire", was also the first-ever Simpsons episode, and aired six years earlier to the day. The writers had been thinking about doing a second Christmas show for many years, but no one wanted to take it on because they thought that they would just be repeating the first episode. After this episode, new Christmas episodes were made almost every year.