The boys plan a Dungeons & Dragons gaming night, which goes with a holiday twist as Leonard sends the group on a quest to rescue Santa Clause from a group of ogres. When Raj dies on the first round of the game, he is out of the game ... giving him the opportunity to go on girls' night with Penny, Bernadette, and Amy. While out at the nightclub, the girls decide to hook Raj up with someone at the bar.
Back in the apartment, the guys trigger an uncontrollable burst of Christmas cheer and memories from Sheldon. Finally, however, the guys get to Santa, but Sheldon decides to betray his comrades to extract revenge upon St. Nicholas, leaving him to the ogres.
This Episode's Science
Particle Accelerator - Sheldon describes his holiday memories in which he was trying to build a particle accelerator out of LEGOs. A particle accelerator is a means of accelerating particles, such as electrons, to high speeds, typically so you can collide them into other objects, possibly another beam of particles, in order to obtain scientific results.
Sheldon: [Explaining how he figured out that the song "Good King Winceslass" was the answer to a riddle posed by Leonard.] It was simple. I combined a well-known historical fact about Bohemia with the memory of my grandparents, Mee-maw and Pop-op, singing Christmas carols while I sat in front of the fire and tried to build a high-energy particle accelerator out of LEGOs.
Leonard: Come on, Sheldon. You know all the Christmas stories and the carols. You've got an eggnog mustache going on there. Just admit it! You're getting a little Yuletide spirit.
Sheldon: Oh, don't be silly! Christmas is a bunch of baloney created by the tinsel industry. Why is this so important to you?
Leonard: Honestly, because I had enough crappy Christmases as a kid, and I'm tired of you sucking the joy out of them now.
Stuart: What's so bad with them?
Leonard: I grew up in a house of crazy academics. Instead of leaving Santa milk and cookies, we had to leave him a research paper. And, in the morning, you could tell he'd been there because the paper had been graded.
Sheldon: No wonder you love Christmas. That sounds amazing!
Leonard: It wasn't amazing. I got a C- four years in a row.
Sheldon: Yeah, I'm familiar with your work. C- was your gift.