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

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.

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.

Sheldon beta-tests an MIT invention after hearing it can help him read people’s emotions. Also, Leonard can’t hide his feelings when Penny announces her brother is coming to town, and Raj invites his ex-girlfriends over to give him dating advice.

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.

Sheldon pushes himself to the limit when he collaborates on projects with Leonard and Wolowitz as well as Amy on the same day. Also, Bernadette is nearing the end of her maternity leave and must return to work.

Howard and Bernadette have a hard time leaving Halley in day care when Bernadette returns to work. Also, Bert introduces the gang to his new girlfriend, Rebecca.

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.

Colonel Williams, an Air Force representative from the Department of Material Command sits down to talk with Wolowitz.

Sheldon and Amy visit Leonard and Penny for the first time since the holidays and share details about their terrible trip to Texas.

Leonard asks Penny for advice when his new relationship starts moving too fast.

Sheldon becomes Leonard's teacher in order to understand football, while an incident with flying a kite threatens Howard and Raj's friendship.

Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.

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.

After Sheldon’s mother and Leonard's father share an evening together, everyone deals with an awkward morning the next day. Also, Penny’s family arrives for the wedding ceremony, including her anxiety-ridden mother, Susan, and her drug dealing brother, Randall.

Tensions rise when the boys struggle to complete their government project on time and Sheldon tries an energy drink to stay awake. Also, Penny and Amy go to a “party” at Bert the geologist’s house, and Koothrappali learns Bernadette’s true feelings about her pregnancy when they clean out the future baby room.

Howard and Bernadette welcome their new baby and Sheldon and Amy celebrate Amy’s birthday.

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

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.

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.