Sheldon and Wolowitz plan birthday celebrations for Amy and Halley, respectively. Also, Leonard receives a Christmas letter from his brother that causes him to spiral out about his own lack of accomplishments.
Extended PlotWhile Howard, Leonard and Sheldon are looking through the comic book rack, Sheldon inquires whether Stuart has the new Aquaman comic and whether he can smoke some meat in his back room. He is planning a historically accurate western meal for Amy’s birthday since she loved “Little House on the Prairie”. Leonard thinks that it’s weird that he is suddenly getting into Aquaman. Sheldon wants to start reading the aquatic superhero before he suddenly becomes cool. Leonard asks about Halley’s birthday and Howard isn't planning anything since Bernadette is on bed rest and he is lazy. Raj enters the shop, greets the guys and barely acknowledges Howard. Howard calls Raj a baby and Raj reacts telling him to grow up. Stuart pleads with them to stop fighting until he learns that Raj is letting him use his extra ticket to the new Star Wars movie. Stuart changes his opinion to that Howard and Raj had a good run together.
In the Caltech cafeteria, Raj asks Sheldon and Leonard whether they want to see “The Last Jedi” again that night. Sheldon does so he can catch the parts he missed while he was blinking. An exhausted Howard shows up announcing that Halley will have a birthday party because anyone who is not a heartless monster and Bernadette would want one. He gives Leonard and Sheldon invitations and doesn’t invite Raj. Sheldon is planning to come, but doesn’t like those sugary flowers on birthday cakes. Howard doesn’t invite Raj and doesn’t think that it means a thing that he is Halley’s godfather. Raj quickly leaves.
Penny enters the Hofstadter apartment reading a letter, the Christmas letter from Leonard’s brother telling about their great life making Leonard feel bad. Sheldon enters carrying a butter churn for his dinner for Amy and wants to store it in 4A. Penny quips that she already got Amy a butter churn. He is making hardtack, boiled salt pork and a gob of chew-able tree sap. And afterwards they will have their annual birthday coitus. Penny wonders if their sex will be historically accurate. Leonard assumes that like frontier life, it will be exhausting and short. Sheldon calls Leonard exhausting and short and then leaves.
At the comic book store Howard runs in and invites Stuart to the party which is obvious since he lives there. Howard asks him to bring a few things: balloons, streamers, ice, snack, a bounce house, a face painter and some kids from the "Daddy and Me" class that he never attended. They had gone to the movies. Stuart tells him to not stress about the party since Halley will never remember it. Stuart still says that he’ll help him out.
Amy returns home and finds all the lights out. Sheldon is using candles and tells Amy that he doesn’t know what electricity is since he is a farm boy from a little house on the prairie. Amy screams in excitement. She thinks that everything is perfect. Though tomorrow is her birthday, tonight she gets her authentic frontier dinner from scratch. Amy hugs Sheldon calling it amazing. She sits down because she is starving. Sheldon even churned his own butter, though there is very little of it and it took him nine hours to make. Amy is so excited; she doesn’t think she can wait until midnight to have sex with him. Sheldon replies that she will be glad to have waited because everyone knows that the best foreplay is an adherence to a strict schedule.
Penny returns from work and finds Leonard wanting to make their Christmas letter. He wants to make a list of the cool things they did that year. Penny starts that their jobs are going great though Leonard lost their project to the Air Force and Penny hates her job. “Still employed” starts the list. Then they had their second anniversary, which they forgot to celebrate. “Still married,” was then added. They also almost went to the beach and almost went to the mountains.
Howard shows up at Raj’s new place to invite Raj and then asks him to plan the party. Stuart was having a colonoscopy at the free clinic since an appointment opened up and backed out. Raj is insulted that Howard would only apologize because he needed something. Raj will do it, but only for Halley because she is his goddaughter.
Amy finishes her meal and declines any more. There is plenty of pork fat left over though they could turn it into soap. Amy thinks that that might taste better. Amy moves over to the couch as Sheldon wants to go to stage 2, the pitching of woo. He has some bawdy nineteenth century limericks which Amy interrupts asking if it was getting hot in the room. She wonders if there was something wrong with the food since her stomach felt weird. Sheldon is starting to feel bad too and wonders if it is sexual arousal. He runs off to the bathroom to get sick as Amy heads for the kitchen sink.
Howard comes out onto the porch and finds Raj working on an almost completed party. He can't believe what Raj did overnight. Raj reminds him that he did it for Halley. Howard adds that he is sure that she appreciates it of she knew what was going on and who he was.
In their bedroom, a still sick Sheldon wishes an also sick Amy a happy birthday. Neither had slept the previous night. Sheldon asks if she wanted to make love. Amy only wants to do it if he doesn’t touch her. Sheldon says, “Fine”, pauses a moment and then asks if she wants to do it again.
Penny comes out in the morning and finds Leonard working on their Christmas letter list. He had added “Kept fern alive” and “Assembled “IKEA furniture.” Penny doubted that brown plant was still alive. And she thinks that their lives are great together, so why is it bothering Leonard? He thinks that they are stuck in their lives. They are married two years and should move ahead to buying a house or having a kid. Penny is happy with staying thin and putting money in the bank. So what do they want to do next? How about a big trip? Instead they decide to go to Catalina Island. Sheldon then runs in to use the bathroom since Amy is already in theirs.
At the party, Howard learns that Bernadette’s sister’s kids are sick and aren’t coming. Bernadette calls down and asks how the party is coming. Great? Raj wonders where all the "Daddy and Me" kids were.
Back in the sick room, Sheldon just remembered that he left all the food out. Amy says sarcastically wondering if it was going to go good. Amy lists all her symptoms and Sheldon comments that he is feeling better too.
Sitting alone at a table, Howard calls the party a disaster. Raj complains that he called in a lot of favors to get a Wonder Woman bouncy house. Then he admits that it is a Chinese knock-off called Happy Strong Swimsuit Lady. Raj then climbs into the bouncy house just to have it used to celebrate Halley’s birthday. Howard joins him and starts to argue with him. Howard is stressed out and Raj worked hard on the party. Raj pushes Howard down who jumps up and pushes Raj. Howard is angry about Raj walking out on their friendship. Raj complains about Howard making fun of him all these years. As they get in a shoving match, they find it fun and make up in the process.
Later the gang is at the party while Sheldon and Amy arrived fully recovered. Bernadette calls them all upstairs because Halley is now awake. Sheldon and Amy stay. Sheldon mentions that it is still Amy’s birthday and that the bouncy house is empty. He suggests using it and then finding an unused bedroom upstairs to have their annual love making celebration. Amy agrees as they gleefully head for the bouncy house.
- Guest starring:
- Teleplay: Dave Goetsch, Maria Ferrari & Jeremy Howe
- Story: Steve Holland, Eric Kaplan & Alex Ayers
- Title Reference: The title refers to the consequences of both celebrations, Halley's birthday party and Amy's birthday dinner.
- Taping date: November 21, 2017
- This episode was watched by 13.74 million people with a rating of 2.6 (adults 18-49).
- Total viewers including DVR users xx.x million.
- The Big Bang Theory was ranked #3 for the week ending 16 December 2017.
- This episode aired in Canada on December 14, 2017.
- Chuck Lorre's vanity card 
- masterguyarjun of KIS - The holidays are always a fun time to watch The Big Bang Theory. A few seasons ago, Sheldon ditched opening day of Star Wars: The Force Awakens to show Amy how much she meant to him by starting a tradition on her birthday. There’s nothing like the slow burn of annual coitus to get into the holiday spirit! And last year, Halley was born, introducing a new, albeit purposely absent, addition to the core group. This year, things are slightly different. Halley is 1 year old and remains off-screen along with her bedridden mother. Howard and Raj are determined to stay in a fight. Leonard and Penny struggle to figure out what they are doing with their lives (I’ve been wondering too), and Sheldon is preparing the best birthday Amy has ever celebrated. Sadly, instead of blissful love making, the night ends in horrific puking. 
- IMDb user reviews 
- This episode will be the third time that Amy's birthday is celebrated. (Coitus and/or dinner party).
- The first on screen appearance of Raj's new apartment that is over Bert's garage.
- Howard and Bernadette conceived Halley on Sheldon's bed. And Bernadette gave birth to her on Amy's birthday, spoiling Sheldon and Amy's plans. Sheldon and Amy had revenge by having sex in Howard and Bernadette's house on Halley's birthday.
- Halley will be a little more than a year older than her younger sibling.
- Leonard's brother is revealed to have several children.
- Bernadette does not appear on screen in this episode due to being on bed rest, though she is heard from her and Howard's bedroom at Halley's birthday party. During the production of this episode, Melissa Rauch was in the final stages of her pregnancy, the producers gave her a voiceover role to allow her character to appear whilst explaining her lack of on-screen presence. Production of the show then took a two-week hiatus for Christmas break and to allow Rauch to give birth to a child.
- Howard and Raj made up and apologized in this episode.
- Sheldon: Uh oh!
- Amy: What?
- Sheldon: I left the food out.
- Amy: You afraid it's gonna go *good*?
- Sheldon: So, can I get you anything else?
- Amy: No thanks, I think I'm good.
- Sheldon: You sure? There's still plenty of pork fat. Although if we don't eat it, I suppose we could turn it into soap.
- Amy: That might taste better.
- Amy: I know we only have coitus on my birthday, but I don't know if I can wait until midnight.
- Sheldon: Oh, well, you'll be glad you did. Everyone knows the best foreplay is rigid adherence to a strict schedule.
- Leonard: Well, we've been married two years. Should we think about what's next? Like buying a house or having a baby?
- Penny: Look, I want to do all those things someday, but there's a bunch of stuff I want to do first.
- Leonard: Okay, like what?
- Penny: I don't know, stay thin and have money.
- Raj: You know how many favors I had to call in with my bounce house guy to get Wonder Woman?
- Howard: Is that Wonder Woman?
- Raj: Technically, it's a Chinese knockoff called Happy Strong Swimsuit Lady.
- Howard: Then I take it back; it's a great party.