At the university, Sheldon is educating the guys that Superman cleans his uniform by flying into the sun. Howard questions what happens if he gets something Kryptonian on it. Sheldon is pretty sure that all Kryptonian condiments were destroyed when Krypton exploded. Leonard points out that Superman's sweat is also Kryptonian, and Howard laments over what to do about Kryptonian pit stains. Sheldon counters that Superman doesn't sweat on Earth, and could always wash his clothes while visiting the shrunken Kryptonian city of Kandor, where he has no superpowers and his clothing wouldn't either.
A scientist, David Underhill walks in. Not only is he a winner of the MacArthur Genius Grant (it's a real thing), but even according to Sheldon, his observation of high energy positrons has provided the first conclusive evidence of the existence of dark matter. Everyone but Leonard seems to respect him. Sheldon points out that Underhill's discovery has essentially made Leonard's line of research useless. Leonard points out that Underhill was just at the right place at the right time. Underhill approaches Leonard and asks if he has time to work with him. Leonard is thrilled and gives him all his phone numbers, including his parent's number in New Jersey.
Leonard arrives at the apartment, missing Wii Bowling Night. Dave is very cool, as he is a Black Diamond (advanced) skier, collects vintage motorcycles, and does a spot-on impression of Stephen Hawking having phone sex. Dave and Leonard are getting along very well and are going to the gym the morning. Penny asks if the guys are putting up a Christmas tree to which Sheldon explains. "We do not celebrate the ancient pagan ritual of Saturnalia. Sheldon explains, "In the pre-Christian era, as the winter solstice approached and the plants died, pagans brought evergreen boughs into their homes as an act of sympathetic magic to guard the plants and preserve their essences until spring. This custom was later appropriated by northern Europeans and eventually becomes the so-called Christmas tree." Howard quips "And that, Charlie Brown, is what boredom is all about."
Penny says that she'll put their presents under her tree. Sheldon is upset, stating that Penny is not giving him a present, rather an obligation. He must give her something of equal value based upon on her present and her perceived level of friendship. Sheldon ponders if obligations such as this are a contributing factor to the increased suicide rate during the holidays. Raj and Howard end up taking him to the mall.
Leonard and David are heading up the stairs helping Leonard after the motorcycle fell over on his leg. They run into Penny who is surprised that David is a physicist and they became quickly smitten with each other. Penny claims to be a geek who would love to see his lab. David proposes to take her out to dinner and up the coast his bike. Leonard is left on his own to figure out what just happened.
Sheldon's shopping does not go well in a bath & body shop which is a "cacophonous assault of eucalyptus, bayberry, cinnamon, and vanilla." To be fair, though, it is less scary than the Build-a-Bear shop next door. Howard picks a gift basket to purchase, but Sheldon stops him. He has no knowledge of what size gift basket to get. He experiments by "giving" the gift basket to the sales clerk. Since she acts just like Penny, Howard claims that they'll take it.
Leonard gets a little shock in the university's cafeteria finding Penny with David and having taken his offer of looking around the labs even though he had also offered to show Penny around. David is totally into Penny, saying she has an agile mind (among other things) and he has forgotten about working with Leonard. He is more interesting in doing some research with Penny about the effects of tequila shots on a gorgeous 22-year-old woman.Back at the apartment, Leonard is upset and lying on the couch when Raj and Howard enter carrying several huge gift baskets. Sheldon's plan is to open Penny's gift first, then excuse himself with some "gastric trouble," and get the appropriately-priced basket, returning the others later. Howard wonders if Leonard has already gotten Penny the perfect gift; a new boyfriend.
Leonard goes over to Penny’s finding her drinking rum and eggnog minus the eggnog. He demands an answer to why Penny is suddenly dating someone smarter than himself when she thought he was too smart for her, the very thing that broke them up at the beginning of the season. Penny bursts into tears wondering why he was yelling at her. Leonard immediately retreats and tries to find out what's wrong. She says that David is an idiot because he should have taken the nude photos of his wife off his cell phone before taking nude photos of his girlfriend. Leonard asked about the nude pictures to which Penny responded, “THAT'S what you got from that? The guy is married!" Penny also asks that if he is 'perfectly happy' with the way things are, then why is he jealous. Leonard apologizes and asks her to give him this one since it is Christmas. They end up cuddling. She relents and wishes him a Merry Christmas. Then Leonard brings up that his leg is still in pain.
Later Penny brings over her Christmas presents. Sheldon gets a napkin, which when turned over was signed by Leonard Nimoy. "To Sheldon, Live Long and Prosper." First he is speechless and then Penny apologizes that it is dirty because he wiped his mouth on it. Completely overwhelmed and emotional, Sheldon then exclaims that he now has the DNA of Leonard Nimoy and can grow a clone of his own before quickly running off to his room. Leonard gives Penny a set of children's science experiments because she told David she was so into science. Leonard gets some motorcycle lessons to prevent any future accidents. Sheldon returns to the room with all of the gift baskets he bought and gives them to Penny, much to her surprise; however, thinking that it still doesn't equal the value of his gift, Sheldon gives Penny something he rarely gives anyone... a hug. Leonard considers this day is a Saturnalia miracle (i.e. Sheldon version of a Christmas miracle).
- Guest starring:
- Teleplay: Eric Kaplan & Stephen Engel
- Story: Stephen Engel & Daley Haggar
- "As a Christmas episode this definitely contains the feel good factor, but more than that it is the best episode this season. Combining character development and humor in a blend which this show can do really well." - The TV Critic's Review
- IMDb user reviews.
- Title Reference: The title refers to Sheldon's present and strategy for his Christmas present to Penny.
- Chuck Lorre's vanity card 
- This episode was watched by 11.42 million people with a rating of 4.1 (adults 18-49).
- Episode transcript 
|Sheldon sports a light blue TV Test Pattern (vertical stripes) tee , his ManBot t-shirt, arguably his favorite as it is the one he has worn in more episodes than any other - and in more colors (green, blue, and purple). Also a plain dark maroon tee, and his purple shirt with the Philips/Stooble test pattern.|
|Leonard wears the Brown Sound Fly Lower shirt from Urban Outfitters (looks like a tree with root system - it's discontinued), a red periodic table shirt, a black tee with a squirrel from an unidentified wildlife sanctuary, an unidentified shirt featuring two gold fish, and his yellow APS t-shirt .|
Superman: Man of Steel
|Leonard Nimoy's autograph|
Penny: Hey Sheldon. Are you and Leonard putting up a Christmas tree?
Sheldon Cooper: No, because we don't celebrate the ancient pagan festival of Saturnalia.
Howard Wolowitz: Gather round, kids, it's time for Sheldon's beloved Christmas special.
Sheldon Cooper: In the pre-Christian era, as the winter solstice approached and the plants died, pagans brought evergreen boughs into their homes as an act of sympathetic magic, intended to guard the life essences of the plants until spring. This custom was later appropriated by Northern Europeans and eventually it becomes the so-called Christmas tree.
Howard Wolowitz: And that, Charlie Brown, is what boredom is all about.
Penny: Dave is not smarter than you. He's an idiot.
Leonard Hofstadter: Really? (smiling) Why would you say that?
Penny: Because a smart guy takes the nude photos of his wife off his cell phone before he tries to take nude photos of his girlfriend.
Leonard Hofstadter: He tried to take nude photos of you?
Penny: That's what you took from that?!!
Sheldon Cooper: (after opening Penny's gift) Oh... a napkin...
Penny: Turn it over.
(he does, and is so shocked that he has to grab the chair to keep from falling over)
Sheldon Cooper: "To Sheldon, live long and prosper... Leonard Nimoy."
Penny: Yeah, he came into the restaurant. Sorry the napkin's dirty. He wiped his mouth with it.
(Sheldon stands up quickly, shocked again)
Sheldon Cooper: I possess the DNA of Leonard Nimoy?!
Penny: Well... yeah, yeah, I guess. But look, he signed it!
Sheldon Cooper: (very excited) Do you realize what this means? All I need is a healthy ovum and I can grow my own Leonard Nimoy!
Penny: Okay, all I'm giving you is the napkin, Sheldon.
Penny: (after getting several gift baskets) Sheldon, what did you do?
Sheldon Cooper: (worried) I know! It's not enough, is it? Here...
(he slowly and awkwardly hugs Penny, who is completely shocked)
Penny: Leonard, look! Sheldon's hugging me!
Leonard Hofstadter: It's a Saturnalia miracle!
- First Christmas episode; the others are "The Maternal Congruence" (S3E11), "The Santa Simulation" (S6E11), "The Cooper Extraction" (S7E11) and "The Clean Room Infiltration" (S8E11).
- In "The Cooper-Hofstadter Polarization", Penny found Leonard's replica of the Bottle City of Kandor in his closet while helping him pick out clothes. Superman keeps the bottled city safe in his Fortress of Solitude.
- David Underhill won the MacArthur Genius Grant in 2007.
- In claims of intellectual superiority, David Underhill is to Leonard as Dennis Kim is to Sheldon.
- Leonard's rant about David Underhill references Phineas Gage.
- Sheldon's "know it all" topic this episode is about the history of the Christmas tree.
- When Leonard leans at the apartment's door, Sheldon opens the door saying "Yes" and stands aside while Leonard falls. One normally opens the door and stands in front of it, if not expecting the knock, not aside. If Sheldon would have stand in front of the door then Leonard would have felt on him.
- First appearance of Penny at Caltech.
- After David Underhill and Penny leave Leonard in the Caltech cafeteria, you can see the water bottle's brand name has been altered from "Fiji" to "Biji".
- Strangely, none of the guys seemed to know that Dave Underhill was married; a fact that would have likely been known at least to some at the university, as Dave was a high-profile new arrival there.
- Sheldon frequently mentions/brgas about owning the napkin in future epsiodes, most pointedly when Will Wheaton is around.
- Sheldon gives out one of his rare hugs for Penny.
- Dr. Gablehauser is mentioned by David but he does not appear.