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.

Wil Wheaton interviews Sheldon for a Star Trek documentary where he reveals the ring and his plan to propose to Amy. Bernadette wants to start renovating the house and the topic 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, while listening to a Beach Boys song, realizes he cannot get the song or Amy out of his head and realizes how much she has done for him and how much she means to him.

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 (Adam West). This episode marks the series 200th episode!.

Sheldon works up 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.

Howard and Leonard lie to their spouses about seeing a movie premiere, while Raj spills the beans about their lie. Sheldon and Amy go shopping for Sheldon's new laptop.

Sheldon, Amy, Leonard and Penny head to Big Bear and share a cabin. Meanwhile Raj interjects himself into Bernadette and Howard's baby discussion.

Everyone must choose sides when a small argument between Leonard and Sheldon erupts into a heated fight during a group get-together.

The gang goes to a wine bar and runs into Penny's old boyfriend, Zack. Also, Bernadette gets stuck spending the evening with Sheldon when she can't go wine tasting with the group, and things don't go as planned when Raj introduces his new girlfriend, 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 and Mary Cooper. Sheldon's mother and Leonard's father find something in common. Howard gets an unknown email from the Air Force about his invention.