Sideshow Bob gets contracted as this year's mall Santa. Meanwhile, someone is stealing all the Christmas packages off people's front porches.
Five weeks before Christmas, Lenny orders his Christmas gift online. Two days later United Postal Service delivers it, but someone immediately steals it.
Working as a lighthouse keeper, Sideshow Bob is visited by Cassandra Patterson, a neighbor. She tells him she mentioned him in town, and Bob knows he let his guard down around her when two men come visiting, but when Bob tells them to leave threatening them with a speargun, they say his voice is perfect for the role of Santa Claus at the Springfield Mall as Santa Claus. Meanwhile, more people are getting robbed of their delivered gifts.
The Simpsons visit Santa's Village. Bart skips the line to see Santa, and realizes who he really is. Bob tries to strangle him, but he can't because he refuses to break character, comparing himself to Daniel Day-Lewis.
When a plan to trick the robbers with gunpowder fails for Lenny, Lenny writes 'SB' with his blood. When the news is reported, Homer calls the cops to reveal that SB means Selma Bouvier and she is arrested, freeing the recently-held suspects Scott Bakula, Steve Ballmer, and Sandra Bullock.
Bart still suspects Bob, who agrees to help Bart find the culprit by concealing himself in a box which is placed on the porch.
The thief arrives and the family follows the van to a hangar, finding out Waylon Smithers and Mr. Burns were the culprits. Lisa suggests Burns did it because he's depressed. Mr. Burns tells the story of how as a child he was heartbroken one Christmas, when he asked Santa for just a hug and a smile from his parents and they never delivered, sending him to boarding school instead. Bob as Santa convinces Burns that his harsh upbringing made him the success he is today. Burns and Smithers then return the presents.