Our two genius roommates, Leonard and Sheldon, and their friends are back once again (smarter, but no wiser). Last season, Sheldon went soul-searching (on a train, of course) and was prepared to make some substantial revisions on his Relationship Agreement with Amy, when everything changed. Leonard, meanwhile, was off to Vegas with Penny to finally tie the knot in the season finale. Howard finds himself alone with Bernadette after the sudden passing of his mother; while Raj is not only talking to women – he’s getting exclusive with Emily. Together, they will all learn that life is far more complicated outside of the lab as love and friendship never produce predictable results!
Sheldon is confronted by a mystery of the universe he cannot unravel: when a woman wants time apart to think, exactly how much time does that mean, and is there any way to hurry the process along? In Las Vegas, Penny and Leonard march closer to marching down the aisle, but has Penny gotten over Leonard’s infidelity? And if so, will he do anything to un-get her over it?
Leonard confronts the woman he kissed on the North Sea in an attempt to set Penny’s mind at ease. Also, Sheldon films a special episode of “Fun with Flags” after his breakup with Amy, and Bernadette feels guilty about withholding a secret from Penny.
The guys’ science skills are put to the test when they get a flat tire during Leonard’s bachelor party weekend in Mexico. Also, the girls force Penny to finally tell her family that she eloped with Leonard.
Leonard and Penny finally move in together leaving Sheldon very upset with this big change in his life and wishing he could go back to a time when he had no emotions in 2003 before he met Leonard. Raj, Howard and Stuart attempt to form a band.
The guys take a fencing lesson from Barry Kripke and Sheldon finds himself in an awkward position when Kripke expresses interest in Amy. Also, when Stuart struggles to get female customers at the Comic Book Store, Penny, Amy and Bernadette come by to help him out.
In the midst of a nation-wide helium shortage, Sheldon and Leonard take desperate measures to get the supplies they need. Also, Penny and Bernadette download a dating app on Amy's phone to try and find her a new man.
Adam Nimoy, friend of Wil Wheaton and son of Leonard Nimoy, interviews Sheldon for a Star Trek documentary. Sheldon gets off topic and ends up revealing an engagement ring and his plan to propose to Amy. Bernadette wants to start renovating the house and the issue of starting a family with Howard is brought up.
Amy has a formal date which Leonard, Penny and Bernadette secretly spy on. Sheldon has Howard and Raj help him find a new girlfriend since they found Amy for him.
It’s Thanksgiving. Sheldon and Amy go on a lunch date to the aquarium as friends. Howard, Bernadette, Raj and Emily help out at a soup kitchen. Leonard and Penny make their first Thanksgiving dinner as a married couple.
Sheldon has a revelation when he realizes why a song was stuck in his head. Also, Amy invites Dave over for dinner despite their previously awkward date, and Wolowitz and Koothrappali become obsessed with a fan of their band, "Footprints on the Moon".
As the guys prepare to go to the premiere of the new Star Wars movie, Sheldon plans a special event for Amy's birthday.
Leonard visits a psychiatrist so Penny can make a sales call. Stuart moves out of the Wolowitz house. Sheldon works with Raj looking for extra-solar planets.
The gang decides to head to Vegas for the week on a party bus. Sheldon learns about the importance of empathy and saying sorry.
Sheldon is thrilled when his Meemaw comes to visit, but his excitement quickly fades when she butts heads with Amy. Also, Raj meets a new girl at the comic book store who makes him question his relationship with Emily.
Sheldon and Amy host a live Valentine's Day episode of Fun with Flags, Leonard and Penny grapple with getting older, Howard and Bernadette find a surprise in their hot tub and Raj is torn between Emily and the cute girl he met at the Comic Bookstore.
When the gang finds out about Bernadette's pregnancy, they celebrate by singing karaoke. Also, Bernadette is concerned when Wolowitz freaks out over her pregnancy announcement, and Wolowitz is convinced he must make more money to provide for a baby.
After more than nine years together, the gang finally celebrates Sheldon’s birthday, surprising him with a special guest.
Sheldon works up a contract to split their portion of their guidance system invention royalties, but Bernadette does not like how it's done. Raj must again decide between Emily and Claire when they both contact him.
Amy is shocked at a revelation from Sheldon after she buys him a new laptop. Koothrappali sells out Leonard and Wolowitz after they lie to their wives in order to attend an early screening of a movie.
Secrets are revealed when Amy and Sheldon join Penny and Leonard on a weekend cabin trip. Raj is more excited about Howard's and Bernadette's impending parenthood than they are.
Everyone must choose sides when a small argument between Leonard and Sheldon erupts into a heated fight during a group get-together.
Sheldon and Bernadette spend a night together while the rest of the gang goes to a wine tasting party, but things get uncomfortable for Raj when Zack also attends and takes an interest in Claire.
Sheldon hires Stuart to spend the day with Amy when he’d rather go to a movie screening. Also, Leonard’s mother, Beverly, comes to town and Penny struggles to make a connection with her.
Leonard and Penny get remarried in front of their friends (who show up), Leonard's parents, Beverly and Alfred (Judd Hirsch) and Sheldon's mother, Mary, who finds something in common with Alfred. Howard gets an unknown email from the Air Force about his invention.