With Leonard away, Sheldon and Penny spend quality time together sharing intimate secrets. Also, Wolowitz helps Raj get over his ex-girlfriend.
Leonard's friendship with Sheldon is put to the test when he returns from the North Sea. Meanwhile, Wolowitz's relationship with his mother causes an unusual threat to his masculinity.
When the entire gang competes in a scavenger hunt designed by Raj, it brings out the best - and worst - in everyone.
Sheldon seeks revenge after Amy ruins one of his favorite movies. Meanwhile, Leonard discovers a way to get Penny to do anything, and Raj and Stuart create online dating profiles.
Sheldon must decide how much "Amy time" is too much after she takes a job at his university. Meanwhile, Howard finds himself sleeping on Raj's couch after a fight with Bernadette.
Sheldon's major scientific breakthrough makes him feel like a fraud. Meanwhile, Howard's romantic gesture to Bernadette causes Penny to step up her game with Leonard.
Sheldon feels slighted when Professor Proton seeks advice from Leonard instead of him, and he seeks revenge by befriending a rival science TV host, Bill Nye. Meanwhile, Raj gets jealous when Howard crashes "girls' night".
Leonard tries to keep Sheldon from overreacting when a past mistake comes to light, but Sheldon punishes Leonard by making him walk a mile in his shoes. Meanwhile, Penny confronts Raj's ex-girlfriend, Lucy.
Sheldon protests when the gang drags him to Mrs. Wolowitz's house for Thanksgiving. Meanwhile, Penny and Leonard must deal with a mistake from her past.
Leonard and Amy help Sheldon cope with the shame he's feeling after his accidental contribution to science is disproved. Meanwhile, Raj must stay with Howard and Bernadette for a week.
While Sheldon is away in Texas, everyone gathers to decorate the apartment Christmas tree, and they each realize how much he has changed their lives.
When Penny's big acting break on NCIS is a bust, Leonard struggles to help her, which results in Penny asking Leonard a bold relationship question. Meanwhile, Sheldon tries to learn how to be funny and Raj tries to work on his "game" before talking to girls.
Sheldon tries to relax after he is forced to take a vacation. Meanwhile, Leonard struggles to be supportive of Penny after she quits her job, and Bernadette seeks Stuart's help in replacing one of Howard's comic books.
After the guys can't get Comic-Con tickets, Sheldon tries to hold his own convention and winds up spending a wild night with James Earl Jones. Meanwhile, the girls see if they can act like "grown-ups".
Love is in the air when Sheldon and Amy join Howard and Bernadette for a trip to wine country. Meanwhile, Leonard and Penny must rush Raj's dog to the vet.
Leonard buys a dining room table and it causes Sheldon to reevaluate the changes in his life. Meanwhile, Wolowitz is offered a chance to go back to space and Bernadette struggles with whether or not to encourage him.
After the insults fly, Bernadette tries to broker the peace between Wolowitz and Sheldon. Meanwhile, Penny is offered an embarrassing movie role and Raj asks Amy to write to a woman on his behalf.
When Sheldon visits his Mom in Houston, he is forced to confront a new reality. Meanwhile, Raj's 'Murder Mystery' party starts some fights within the gang.
While Raj is wracked with guilt when he tries to date two women at once, Penny wrestles with whether to take a role in a cheesy movie and Sheldon is torn trying to choose between two gaming systems.
Sheldon faces a personal crisis after deciding he's wasting his time with string theory. Meanwhile, a double date between Raj, Emily and the Wolowitzes ends in embarrassment for Howard.
When Sheldon tries to be spontaneous, it leads to unexpected friction between Penny, Amy and Bernadette. Meanwhile, Raj seeks Howard's help in preparing for a date with Emily.
Professor Proton helps Sheldon cope with grief, while Leonard turns a relationship milestone into a competition with Penny. Meanwhile, Amy and Bernadette make a "Star Wars Day" gift for the guys.
Bad day causes Penny to reevaluate her life choices - including Leonard. Meanwhile, Howard and Bernadette struggle to care for Mrs. Wolowitz, and Raj gets relationship advice from Sheldon.
Sheldon is forced to confront an uncertain future and considers a major move. Meanwhile, Raj and Emily take it to the next level, and Mrs. Wolowitz's injury is a major headache for Howard and Bernadette.