Penny runs into her ex-boyfriend Zack, who has gotten rich from selling his company and married a similarly dim-witted woman named Marissa. Meeting with Leonard and Penny, they say Zack is infertile and ask to pay Leonard as a sperm donor so they can have a baby. Leonard is flattered, but Penny finds it creepy. Leonard says that since Penny decided she did not want to have children, he should be allowed to help another couple with this issue. Sheldon advises him to think about the emotional toll this could have on him. Leonard says he will not do it if Penny objects; Penny says she will support whatever decision Leonard makes. Meanwhile, Raj tries to get Anu back but she points out he just wanted to be married like his friends. Raj points out that Anu is similarly looking for a quick marriage. He admits to Anu that he really likes her and they decide to start their relationship as just dating.
Sheldon's mother Mary refuses to attend his wedding unless he invites his older brother George, with whom he is no longer speaking. Sheldon and Leonard fly to Texas to talk to George, who now owns a chain of tire stores. He refuses to attend and later explains to Leonard and Sheldon that the family sacrificed a lot to fund Sheldon's education, and he was stuck caring for their mother and sister Missy after their father died while Sheldon was in college. Sheldon never thanked him for this. Leonard takes George back to the hotel room where Sheldon apologizes for what he did and the brothers reconcile. George agrees to attend the wedding. Meanwhile, Howard and Bernadette's children contract pinkeye, infecting everyone except Penny, much to Amy's fury.
After learning Sheldon went behind their backs to work with the military again, Leonard and Howard say Sheldon is like Thomas Edison, taking credit for others' ideas, while they are more like Nikola Tesla. Leonard and Howard bring in Barry Kripke to help create a better idea than Sheldon's, but Kripke goes to the military himself, cutting all three of them out. Meanwhile, Bernadette fears Ruchi is trying to steal her projects at work while she is on maternity leave and enlists Raj to spy on her. Though he finds proof that Ruchi may be stealing from Bernadette, Raj tries to defend Ruchi like a boyfriend would, pointing out Bernadette's hypocrisy as she would most likely have stolen from other people's projects as well. Ruchi is not happy about this and promptly dumps Raj.
Two months after the events of "The Change Constant", Sheldon and Leonard repair Sheldon's DNA molecule model as everyone prepares to fly to Sweden for the Nobel Prize award ceremony. Howard and Bernadette nervously leave their kids for the first time with Stuart and Denise, while Raj leaves his dog with Bert. Penny has become pregnant, though she and Leonard are keeping it a secret. On the flight, Raj thinks he spots Sarah Michelle Gellar. Penny's frequent bathroom trips make Sheldon fear she is sick. Leonard reveals the pregnancy to Sheldon, but instead of being excited for Penny, Sheldon is only selfishly relieved that he will not get sick and he exposes the pregnancy, offending Leonard. At the hotel, a series of minor incidents with their kids make Howard and Bernadette want to go home. Much to their dismay, Sheldon is still insensitive. Amy furiously tells Sheldon he broke their friends' hearts and they only tolerate him because he does not intentionally do so, which she also sometimes does. Everyone decides to stay for the ceremony and Raj brings Gellar. After they are awarded their medals, Amy encourages girls to pursue science while Sheldon thanks his family and then individually acknowledges each of his friends and Amy as his other family who always support him. The episode closes with the gang eating in Apartment 4A (an allusion to the final scene in the opening credits) as an acoustic version of the theme song's chorus plays.
Sheldon is annoyed that Amy does not have time to work on the super-asymmetry project with him so he talks President Siebert into getting her removed from her own project at the university. Amy is angry at both of them as she wants to still have her own identity outside the marriage. When confronted by Amy, Siebert apologizes to her but states that it will be difficult for the university to give her her project back. After talking with Arthur Jeffries in a dream, Sheldon apologizes to Amy and both of them talk about their fears in their marriage. Meanwhile, Raj does not want to have Howard join him in his show at the planetarium, thinking he'd just use his astronaut status to make it about himself. Raj eventually lets him join in and Raj and Howard spend the whole time complimenting each other, surprising Bernadette, Leonard and Penny.
The Big Bang Theory is an American television sitcom created by Chuck Lorre and Bill Prady, both of whom served as executive producers on the series, along with Steven Molaro. All three also served as head writers. The show premiered on CBS on September 24, 2007 and concluded on May 16, 2019, having broadcast a total of 279 episodes over 12 seasons.
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