"The Santa Simulation" is the eleventh episode of the Season 6 of The Big Bang Theory. Dakin Matthews guest stars as Santa Claus.
The gang leave the girls out of a Dungeons & Dragons game and they all have girls-night which Raj crashes, after his character dies early on. Meanwhile, during the game, Sheldon explains his past Christmases as a youth, which end up revealing why he hates the holiday so much.
Leonard builds a cardboard fireplace for his apartment, despite getting a paper cut. He tells Penny that the guys are playing Dungeons & Dragons together. Penny asks him if he'd rather play a fantasy board game on a Saturday night rather than be with his girlfriend who let him have sex with her. Meanwhile, Sheldon tells Amy that she isn't invited to play D&D, although she always wanted to play D&D. Bernadette tells Howard that she worked late so that they could be together on Saturday night. Howard tells her that if he doesn't come, then the guys will blame the failure of their night on her. Furthermore, Raj and Stuart originally planned to have dinner, but are more excited about joining the game.
The guys' D&D quest starts with Leonard giving a Christmas gift to Sheldon who complains about Christmas, like the overuse of "t'is" and "t'was". Nevertheless, he pulls out of the scroll from the Christmas stocking that explains their quest starts in a village of massacred elves. They must rescue their leader Santa Claus from a pack of ogres. On Leonard's idea of making a holiday-themed quest in D&D, Sheldon replies that it was like a sandwich of grape jelly and petroleum jelly. In-game, they follow the trail of broken candy canes where Howard finds a secret door, plans to set up an invasion strategy, but Raj rushes in anyway where it is a dark room filled with weapons. He hits a tripwire that triggers a cannon, killing him and also disqualifying Raj out of the game. Raj protests, and asks for resurrection rods, which they refuse.
Penny leads the girls into the apartment to act like runaway model fashion models. Raj asks to come, but first they tell him that he can't come because its girls' night. But Penny invites him.
At the nightclub bar, the girls plan for Raj to find a girl to get laid, hook-up with or a quality relationship. Raj finds a hot girl at the bar they talked for a while, and he leaves her to return to the girls. He finds that she gave him a phony email address. Raj complains that is really his fault since he falls for girls that are out of his league. He did when he fell for his friends' hot girlfriends, Penny and Bernadette. Amy then concludes at some point he'll fall for her. Raj says a definite "no", but Penny and Bernadette urgently try to get Raj to change his comment about Amy, but he keeps saying "no", and that he wouldn't fall for her. Later, he apologizes to Amy if he upset her. After a conversation, Amy tells him that he'll eventually find somebody where Raj hopes that she is as half as a lovely person as Amy. She tells the girls they can leave, obviously getting back at Raj who then tells Penny that now he may fall for Amy, leaving her confused and disgusted.
Meanwhile, during D&D, the characters find a large chest. The door locks behind them, and glowing words appear on the chest as the walls start to close in. Thanks to the clues given, Sheldon figures out the answer and sings "Good King Wenceslas" which stops the walls from closing in. Sheldon knows the song from when his grandparents would sing carols at Christmas time. They tried to resume the game, but Sheldon insists on singing the remaining verses. After a while, he finishes singing the song, they find a pool of melted snowman. Outside the game, Sheldon picks up a cup of eggnog. Leonard says he's glad that Sheldon is getting into the holiday spirit, but Sheldon denies it and claims that he drinks eggnog all year-round. Leonard reveals that his Christmases where bad for him when he was a kid whilst trying to wish Sheldon would get into the spirit. Instead of leaving Santa milk and cookies, Leonard's family left research papers, and in the morning, they were graded by Santa. For Leonard, he gets a C- which he finds displeasing, but Sheldon thinks they must have been great Christmases.
Later, they crack the code to lower the drawbridge. The answer is playing "Jingle Bells" with bells. This act lowers the drawbridge where they find the bloody and beaten Santa in the dungeon. Taking the advantage, Sheldon casts a spell of paralysis on Howard and Stuart, goes in to confront Santa. He confesses that when he was five years old, he asked Santa to revive his grandfather, Pop-Pop, who had died at that time during Sheldon's said age and was the only relative that urged him to follow his dream into science. Instead Santa brought him a set of Lincoln Logs. Sheldon throws away the key, kicks Santa and leaves him to die at the hands of the ogres. Everyone is completely shocked as they now know why Sheldon doesn't like celebrating Christmas, due to a traumatic family tragedy at the time.
That night, Sheldon enters the living room to find Santa Claus leaving him presents and he apologizes for not bringing back his Pop-Pop because according to Santa, his magical power is limited. He has something special for Sheldon, who seems excited. It turns out that Santa is firing a cannon at Sheldon for his revenge. However, it revealed to be Sheldon's nightmare, now realizing he shouldn't blame Santa for his Pop-Pop not coming back to life.
- Title Reference: The title refers the symbolical character being rescued in the gang's Dungeons and Dragons game.