1 Series, 1 Episode
The group of friends face an awkward morning after Sheldon's mother and Leonard's father share an evening together. Penny's family arrive in town to attend Penny and Leonard's second wedding ceremony.
Howard has a meeting with Air Force representative Colonel Williams about the gyroscope he invented with Leonard and Sheldon. Penny carelessly reveals Bernadette is pregnant to her colleagues at work.
The guys work around the clock on the Air Force project, leaving Sheldon fighting to stay awake. Penny and Amy attend a university gathering. Raj learns Bernadette's true feelings about her pregnancy.
When Amy's apartment is flooded, she proposes a 'cohabitation experiment' with Sheldon while it is repaired. Raj finds out the gender of Howard and Bernadette's unborn child before they do.
Leonard and Penny intervene when a cohabiting Sheldon and Amy have an argument about their 'bathroom schedule'. Howard and Bernadette's secret stay-cation is interrupted by unexpected guests.
Penny and Leonard attend a comic book convention, where Penny is surprised to meet fans of her acting work. Sheldon and Amy host a brunch at Penny's flat and Howard makes an impulsive purchase.
Amy lies to Sheldon by telling him the completed repair work on her flat is still ongoing so that they can carry on living together. Penny moves Leonard's collectables into storage behind his back.
Sheldon goes to great lengths to convince Amy that they should have a baby together. Raj feels too embarrassed to tell his friends what the new woman in his life does for a living.
Sheldon can't contain his jealousy when he hears that his university colleague Bert the geologist has won a prestigious fellowship. Howard finds an old remote-controlled toy that he made in the past.
Sheldon, Amy, Leonard and Penny divide up all their possessions into two separate households, but tension ensues. Raj and Stuart compete to become indispensable to Howard and Bernadette.
Sheldon and Amy attempt to celebrate her birthday with an intimate night at home. Bernadette goes into labour, so Howard, Raj and Stuart rush the expectant mother to the hospital.
The gang gather for a post-holiday catch-up and hear all about Sheldon and Amy's terrible trip to Texas, Leonard and Penny's Christmas tree struggles, and Howard and Bernadette's first days as parents
Penny thinks Leonard has stopped making an effort in their relationship so she departs for a spa weekend with Amy. Howard and Raj try to stop the noise made by a squeaky floorboard in the baby's room.
Sheldon tests a newly invented device after hearing that it can help him to read people's emotions. Raj gathers his former girlfriends together so that they can give him some dating advice.
Leonard and Howard attempt to distract Sheldon with a trip to a historic railway when he slows the progress of their work on the Air Force guidance system. Raj and Stuart look after baby Halley.
Amy is furious when she learns Sheldon has shared intimate details of their relationship with his colleagues at the university. Raj considers trying to live without financial support from his father.
Cut off from his father's fortune, Raj struggles to balance his books and decides to appoint Sheldon to organise his finances and get him out of debt. Penny considers joining the guys at Comic-Con.
Leonard and Penny offer Sheldon's old room to Raj when he is forced to move out of his flat to save money, leading to unexpected conflict among the gang and unwanted observations from Leonard's mother
Leonard, Penny and Raj settle into their new living arrangement, but Penny and Raj get along so well that Leonard starts to feel left out. Sheldon and Amy begin to collaborate on a scientific project.
Sheldon pushes himself to the limit when he collaborates on two projects - one with Leonard and Howard, plus another with Amy - on the same day. Bernadette nears the end of her maternity leave.
Howard and Bernadette find it upsetting to leave Halley at the nursery when Bernadette returns to work at the end of her maternity leave. Bert the geologist introduces the gang to his new girlfriend.
Leonard isn't thrilled when he finds out Penny is considering taking a new job that has been offered to her by her ex-boyfriend Zack. Sheldon tries to develop his brain further by learning new skills.
Amy is offered a visiting research fellowship at Princeton University. Raj makes new living arrangements. The guys complete their infinite persistence gyroscope project but events spin out of control.
The gang become concerned about the situation when Sheldon's former admirer, Dr Ramona Nowitzki, resurfaces while Amy is away working at Princeton University