While Leonard is away, Sheldon and Penny bond, but it's Sheldon's feelings that are crushed when Leonard returns from the North Sea. Also, Wolowitz helps Raj get over his ex-girlfriend.

Howard's relationship with his mother causes an unusual threat to his masculinity. Meanwhile, Leonard's friendship with Sheldon is put to the test when he returns from the North Sea earlier than expected.

When the entire gang competes in a cutthroat scavenger hunt designed by Raj that tests their science knowledge and street smarts, it brings out the best – and worst – in everyone.

After Amy ruins one of Sheldon's favorite movies – Raiders of the Lost Ark – he gets defensive, seeking revenge. 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, and their relationship is put to the test. Meanwhile, Howard finds himself sleeping on Raj's couch after a fight with Bernadette.

Sheldon's latest scientific breakthrough makes him feel like a fraud – and threatens to haunt him forever. 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 becomes 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.

An upset Sheldon protests when the entire gang drags him to Mrs. Wolowitz's house for Thanksgiving. Meanwhile, Penny and Leonard must deal with a mistake from her past.

Sheldon faces a crisis after Leonard disproves his accidental scientific discovery. Meanwhile, Raj must stay with Howard & Bernadette 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 for Christmas.

As Leonard tries to help Penny with a disappointment, Penny asks him a bold question about their relationship; Meanwhile Raj and Stuart practice their skills at talking to women and 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 after she quits her job; Bernadette needs to replace one of Howard’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.

On Valentine's Day, 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 after a trip to NASA; 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 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.

Faced with an uncertain future, Sheldon considers a major change; Emily and Raj decide to take things to the next level. Also, Howard and Bernadette struggle to care for Mrs. Wolowitz when she is injured.