Howard is in space and loving it — until he's not. Back on Earth, the couples navigate new stages in their relationships.
Penny worries about her relationship with Leonard and considers breaking up. The commitment question looms.
Sheldon meets a new assistant who challenges him intellectually. Howard adjusts to being back from space.
The girls have a game night while the guys compete in their own way. The split-group dynamic creates parallel storylines.
Halloween at the comic book store brings costumes and competitions. Howard brags about his astronaut experience one too many times.
Sheldon becomes addicted to an online game and Amy tries to intervene. His competitive streak takes over his life.
Sheldon and Amy disagree about living arrangements and their future. Howard tries to navigate married life under his mother's roof.
A mysterious number keeps appearing in Sheldon's life and Penny investigates. The puzzle element adds a fun twist.
A parking spot at the university causes a war between Howard and Sheldon. The tiny space becomes a battleground of principle.
Howard takes Bernadette fishing to bond with her father. Sheldon catches a cold and Amy tends to him with mixed results.
The guys play a dark fantasy role-playing game for the holidays. Raj's character choices reveal more about him than he intended.
Sheldon makes an inappropriate comment at work and has to take a sensitivity seminar. His attempts at human resources compliance are painful.
The guys take a road trip dressed as Star Trek characters and their car breaks down. The detour becomes the adventure.
Sheldon and Kripke team up on a project and Sheldon has to lie about his personal life to keep up with Kripke's bragging.
Leonard accidentally spoils a show for Sheldon and the fallout is massive. The spoiler alert sets off a chain of revelations about the group.
Valentine's Day pushes Sheldon to make a romantic gesture for Amy. Leonard and Penny compare their relationship to their friends'.
Raj reconnects with an old flame and struggles with confidence. Sheldon helps in the most Sheldon way possible.
The guys have to do community outreach at the university and dread it. Their interactions with normal people are enlightening.
A secret is found in Howard's closet and it changes how he sees his father. The emotional reveal is one of the season's highlights.
The university tenure decision pits the guys against each other. Professional ambition strains personal friendships.
Sheldon struggles to let go of unfinished TV shows. Amy tries to teach him about closure, with limited success.
Professor Proton, Sheldon's childhood science hero, appears for a visit. Meeting your idol doesn't always go as planned.
The girls play a fantasy role-playing game and discover they love it. Raj and Lucy's relationship reaches a turning point.
Lucy breaks up with Raj, and the group rallies around him. Leonard gets a career opportunity that could take him far away.