The group struggles through an awkward morning after Sheldon's mother and Leonard's father spend an evening together; Penny's family arrives.
Wolowitz has a meeting with Colonel Williams, a representative from the Air Force Department of Material Command.
Sheldon tries to stay awake with an energy drink as the gang races to finish its government project on time; Penny and Amy attend a gathering at Bert the Geologist's house; Koothrappali learns Bernadette's true feeling about her pregnancy.
After her apartment floods, Amy suggests that she and Sheldon move in together; Koothrappali finds out the gender of Howard and Bernadette's baby before they do.
Things do not run smoothly when Amy moves in with Sheldon, and Leonard and Penny have to intervene; Howard and Bernadette find unexpected guests at their house when they decide to cancel their vacation plans.
Penny learns there are fans of her performance in "Serial Ape-ist" when she and Leonard attend a Comic Con event; Amy hosts a brunch at Penny's apartment; Wolowitz makes an impulsive purchase.
Amy lies about repairs being made to her apartment so she can continue living with Sheldon; Leonard lets Penny decorate Sheldon's old room.
Sheldon is determined to convince Amy they should procreate; Koothrappali is reluctant to tell the gang what the new woman he's dating does for a living.
Sheldon gets jealous when a co-worker wins an award; Wolowitz finds an old remote control Stephen Hawking action figure that he made.
Sheldon and Leonard disagree about how to divide their shared belongings; Koothrappali and Stuart fight to be the most helpful to Bernadette during her final weeks of pregnancy.
While Howard and Bernadette welcome their new baby into the world, Amy celebrates her own birthday with Sheldon.
Sheldon and Amy visit Penny and Leonard after the holidays and tell them about their terrible trip to Texas.
Penny thinks Leonard is taking her for granted and decides to go on a spa weekend with Amy; Wolowitz and Koothrappali try to fix a squeaky floorboard in the baby's room.
Sheldon tests an MIT invention after hearing it can help him read people's emotions; Leonard finds out Penny's brother is coming to town; Raj asks his ex-girlfriends to give him dating advice.
Leonard and Wolowitz try to distract Sheldon when he slows the progress of their guidance system; Raj and Stuart look after baby Halley while Penny and Amy take Bernadette for a night out.
Sheldon and Amy have their first fight since moving in together; Koothrappali is shocked at the realities of financial independence when he stops receiving support from his father.
Cut off from his father's fortune, Koothrappali appoints Sheldon to help him get out of debt; Penny considers joining Leonard at Comic-Con.
Leonard and Penny offer Sheldon's old room to Raj after he moves out of his apartment.
Leonard, Penny and Raj settle into their new living arrangement; Sheldon expresses interest in Amy's work.
Sheldon pushes himself to the limit when he collaborates on projects with Leonard and Wolowitz as well as Amy on the same day; Bernadette nears the end of her maternity leave and must return to work.
Howard and Bernadette struggle to leave Halley in day care; Bert introduces the gang to his new girlfriend, Rebecca.
Leonard is less than thrilled when Penny considers accepting a job offer from Zack, her ex-boyfriend.
After celebrating the completion of the top-secret Air Force project, Leonard, Sheldon and Wolowitz get an unwelcome surprise; Amy receives an offer for a summer position as a visiting researcher.