The aftermath of the parents meeting creates ripples through the group. New family alliances form while old tensions surface.
The guys work on a military project and the secrecy requirements clash with Sheldon's compulsion to share everything he knows.
Raj finds himself dependent on his friends and decides to break free. Energy drinks play an unexpectedly large role.
Sheldon and Amy try living together as an experiment. The cohabitation trial tests both their limits and their love.
A hot tub creates problems when contamination concerns clash with relaxation goals. Sheldon versus recreational water is a classic matchup.
Bernadette is pregnant and dealing with the reality of approaching parenthood. The guys handle the news with varying degrees of maturity.
Penny lies about something and the truth-telling theme cascades through the group. Everyone's hiding something small.
Bernadette has an idea that could revolutionize things, but the execution requires the whole team. Brain and ambition collide.
Bert the geologist wins a prestigious award and Sheldon has feelings about it. The jealousy is both petty and deeply human.
Sheldon and Leonard divide up their shared belongings as the living situation changes. The property split gets emotional.
Bernadette goes into labor and the timing creates birthday synchronicity. The hospital scenes are chaotic and heartwarming.
The holiday episode finds everyone adjusting to new dynamics — a new baby, new living arrangements, and new perspectives on family.
Penny and Leonard's relationship gets a check-up when they evaluate what they really want from each other. Honest conversations follow.
Sheldon builds an emotion-detecting robot and the results are uncomfortably accurate. The machine says what humans won't.
Sheldon asks for a toy train and the request reveals deeper feelings about childhood, comfort, and growing up.
An allowance disagreement between Sheldon and Amy exposes different attitudes about money and partnership.
The group plans their annual Comic-Con trip and logistical nightmares ensue. Getting everyone organized is harder than saving the world.
Raj moves into Sheldon's old room and the revolving door of roommates prompts reflection on who really needs whom.
Amy and Sheldon collaborate professionally for the first time and discover it's harder to work together than live together.
A forgotten memory resurfaces and changes how someone sees a past event. The recollection sparks a group discussion.
Bernadette goes back to work and the separation from baby Halley is tough. Howard steps up in new ways.
Penny runs into an ex-boyfriend and it makes Leonard reconsider his own growth. How far they've all come becomes the real story.
A military project the guys have been working on gets shut down, and the career implications are serious. Sheldon takes it hardest.
A visiting colleague gets too close to Sheldon and Amy's relationship is tested by long-distance temptation. The season ends with a cliffhanger.