Sheldon and Penny share secrets while Leonard is away; Wolowitz helps Raj get over his ex.
Leonard and Sheldon's friendship is tested; Wolowitz's relationship with his mom causes a threat to his masculinity.
Raj designs a scavenger hunt that brings out the best -- and the worst -- in the whole gang.
Sheldon wants revenge after Amy ruins one of his favorite films; Leonard finds a way to get Penny to do anything; Stuart and Raj make online dating profiles.
Sheldon and Amy's relationship is tested when she takes a job at his university; a fight with Bernadette leaves Howard sleeping on Raj's couch.
Sheldon's latest scientific breakthrough leaves him feeling like a fraud; a romantic gesture between Howard and Bernadette causes Penny to up her game with Leonard.
When Professor Proton asks Leonard for help with an experiment, Sheldon retaliates by befriending Proton's rival, Bill Nye.
When a mistake comes to light, Sheldon makes Leonard walk a mile in his shoes; Penny decides to confront Raj's ex.
When the gang decides to spend Thanksgiving at Mrs. Wolowitz's house, Sheldon protests; Leonard and Penny deal with an error from her past.
Amy and Leonard try to help Sheldon deal with his shame; Raj stays with Bernadette and Howard for a week.
While Sheldon is in Texas, the rest of the gang realize how much he has changed their lives as they decorate the apartment Christmas tree.
As Leonard tries to help Penny with a disappointment, Penny asks him a bold question about their relationship; Sheldon wants to learn how to be funny.
Sheldon must learn how to relax when he is forced to take a vacation; Leonard tries to support Penny when she quits her job; Bernadette needs to replace one of Stuart's comic books.
Unable to get Comic-Con tickets, Sheldon tries to hold his own convention and ends up spending a wild evening with James Earl Jones; the ladies try to act maturely.
Sheldon and Amy go on a trip to wine country with Howard and Bernadette; Penny and Leonard rush Raj's dog to the vet.
When Leonard buys a dining room table, Sheldon re-evaluates the changes in his life; Bernadette is torn when Wolowitz gets the chance to go back to space.
Bernadette tries to negotiate peace between Sheldon and Wolowitz; Penny receives an embarrassing offer; Raj wants Amy to write to a woman on his behalf.
Sheldon is faced with a new reality when he visits his mom in Houston; a murder mystery party starts arguments.
Raj struggles with guilt when he dates two women at once; Penny has a chance to play a part in a cheesy movie; Sheldon is torn between two gaming systems.
Sheldon has a personal crisis when he decides string theory is a waste of his time; a double date ends in embarrassment for Howard.
Sheldon gives spontaneity a try, which causes unexpected friction for Penny, Bernadette and Amy; Raj asks Howard for help with preparation for a date with Emily.
Professor Proton (Bob Newhart) helps Sheldon deal with grief; Leonard gets into a competition with Penny; Bernadette and Amy prepare a "Star Wars Day" gift for the guys.
A bad day compels Penny to re-evaluate her choices -- including Leonard; Bernadette and Howard must care for Mrs. Wolowitz; Sheldon gives Raj advice on relationships.