After driving to Vegas to get married, Penny struggles with Leonard’s confession that he kissed another girl. Also, Sheldon doesn't know how to act after Amy pushes pause on their relationship.

Leonard isn’t thrilled when Penny considers taking a new job offered by her ex-boyfriend, Zack.

Leonard jumps through hoops to help secure the perfect wedding venue for Sheldon and Amy. Also, Bernadette and Howard have a hard time deciding who should stay at home with the kids and who should go back to work.

When Amy doesn’t have time to work on super-asymmetry, Sheldon goes to great lengths to ensure she’s available to work with him even it if means accidentally sabotaging her career in the process. Raj doesn’t want Howard to join him in hosting a show at the planetarium.

When Penny feels that Leonard is taking her for granted, she decides to go on a spa weekend with Amy. Also, Wolowitz and Koothrappali try to fix a squeaky floorboard in the baby’s room.

Wolowitz feels nervous when he is asked to throw the first pitch at a Los Angeles Angels game. Penny and Leonard want to prove Sheldon wrong after he says he and Amy are the better couple.

While Sheldon says a tearful goodbye to the final installment of "Fun with Flags", Leonard, Howard and Raj search for something significant in a dead professor's research. And Bernadette finds out what her colleagues really think of her.

When Raj is asked to create a message in case a NASA mission discovers alien life, the guys fight over what he should do. Also, Penny is torn between auditioning for a movie or keeping her successful pharmaceutical sales job.

Sheldon and Amy struggle with picking a wedding date, which stresses out Sheldon and causes him talking in his sleep. Meanwhile, Raj and Stuart fight over the attention of one of Bernadette's co-workers.

When Sheldon won't tell anyone why he's never mentioned his childhood best friend, Leonard takes matters into his own hands. Bernadette and Penny take out Raj’s fiancée for dinner to get the skinny on her.

The concept of what it would mean for women everywhere if Amy were to win a Nobel Prize causes Amy to have a meltdown. Also, Howard and Raj try to relive the good old days after Howard buys a scooter that looks like the one he had years ago.

Sheldon and Amy have their first fight since moving in together, and Koothrappali is shocked at the realities of financial independence when he stops receiving support from his father.

When Raj moves out of his apartment, Leonard and Penny offer him Sheldon's old room.

Leonard, Penny and Raj adjust to their new living arrangement, and Sheldon takes an interest in Amy’s work.

After Leonard, Sheldon and Wolowitz celebrate the completion of the top secret air force project, they are met with an unpleasant surprise. Also, Amy is offered a summer position as a visiting researcher.

As Howard worries about fatherhood, he and Sheldon bond when they jointly assemble a model rocket. Meanwhile, Penny bonds with Leonard's mother, Beverly, much to his concern.

Leonard and Howard are furious after they learn Sheldon went to work with the military behind their backs. Also, while Bernadette is on bed rest, she asks Raj to do some digging when she suspects that Ruchi might be trying to take over her projects at work.

Raj and Howard's feud continues as the gang plan Halley's first birthday party. Sheldon's surprise for Amy's birthday goes awry when they get food poisoning. Also, Leonard gets a Christmas letter from his brother that causes him to spiral out about his own lack of accomplishments.

When Bernadette won't go into labor, the gang tries different tactics to get things started. Also, Howard confronts Bernadette after Amy accidentally reveals she's already chosen their son's name.

Bill Gates visits Penny's work, and the gang schemes to meet him. Hilarity ensues. Meanwhile, Sheldon is convinced that he's a target of an April's Fools prank.

Penny runs into her ex-boyfriend, Zack, who invites her and Leonard to a dinner to meet his newlywed wife. After the dinner the newlywed couple make an odd proposition to Leonard, which makes Penny to freak out. Also, Raj attempts to mend things with his ex-fiancée, Anu.

Sheldon and Amy are thrilled when their super asymmetry theory is proven by two physicists, until they try to kick Amy off the Nobel nomination. Also, Bernadette gets one of her drugs approved at work and wants a reluctant Penny to head the sales team.

Sheldon is thrilled to help Bernadette and Wolowitz navigate bureaucratic paperwork, until he discovers they are breaking the law. Also, Leonard is disappointed when his friends exclude him from a scientific project.

When Penny and Bernadette go to San Diego for a pharmaceutical sales convention, Wolowitz is in charge of the kids. Also, Sheldon finds a book on experimenting on kids, and the guys plus Amy make a day of it.

When competitors Pemberton and Campbell charm America on a publicity tour, Sheldon and Amy try to bring Nobel laureates Kip Thorne, George Smoot and Frances Arnold to their side. Also, Halley's fear of the dark causes opportunity and conflict at the Wolowitz home.