Sheldon and Penny bond over missing Leonard. Howard tries to help Raj get over his breakup with Lucy. Amy and Bernadette take a trip together to a biology convention.
Sheldon feels betrayed when Leonard returns from the North Sea and wants to spend his time with Penny instead of him. Howard's latest foray into helping his mother has some disastrous side effects.
Sheldon gets mad at Amy for ruining one of his favorite movies, Raj and Stuart try to make their online dating profiles more appealing, and Leonard tries to play the sympathy card with Penny.
Howard tries to do something special to celebrate the anniversary of his first date with Bernadette. Sheldon is conflicted when he makes a major scientific breakthrough but some details have to be corrected.
Sheldon seeks payback when Arthur "Professor Proton" Jeffries asks Leonard for help on a project instead of him. Raj gets upset at Howard for crashing his night with the girls.
The gang spend Thanksgiving at Mrs. Wolowitz's house. Howard tries to bond with his father-in-law, and a mistake from Penny's past comes back to haunt her.
After Leonard tries to help Penny following a failed role on a TV show, she makes an important decision. Meanwhile, Raj and Stuart try to practice their social skills, and Sheldon navigates the intricacies of being funny.
Sheldon tries to relax after he is forced to take a vacation. Leonard struggles to be supportive of Penny after she quits her job. Amy receives unwanted attention from a co-worker. Bernadette seeks Stuart's help in replacing one of Howard's comic books.
When the guys can't get hold of any Comic-Con tickets, Sheldon tries to hold his own convention and ends up spending a wild night with James Earl Jones. Meanwhile, the girls try to feel more mature by going to a fancy hotel for tea.
Sheldon and Amy take a train ride to Napa Valley with Howard and Bernadette on Valentine's Day. Leonard and Penny take Raj's dog to the vet when she accidentally eats some chocolate.
Leonard's purchase of a dining room table causes Sheldon to reevaluate the changes in his life. Meanwhile, Howard is offered a chance to go back to space and Bernadette struggles with whether or not to encourage him.
After arguing with Sheldon, Howard tries to make amends by taking him to NASA headquarters in Houston. Penny has second thoughts about quitting her waitressing job when her car dies. Amy gets involved in trying to find Raj a date.
When Sheldon visits his mother in Houston, he is forced to confront a new reality. Back in Pasadena, the rest of the gang reluctantly take part in Raj's Murder Mystery party.
While Raj is wracked with guilt when he tries to date Lucy and Emily at the same time, Penny wrestles with whether to take a role in a cheesy movie and Sheldon is torn trying to choose between two gaming systems.
Penny tries to help Sheldon when he reconsiders his "relationship" with String Theory. During a dinner with Howard and Bernadette, Raj discovers Howard once embarrassed himself on a date with Emily.
When Sheldon tries to be spontaneous, it leads to unexpected friction between the girls. Meanwhile, Raj seeks Howard's help in preparing for a date with Emily.
Penny gets fired from her movie and takes a serious look at her life. Raj sees Emily on a date with another man at the movies. Howard and Bernadette have to take care of his mother after she breaks her leg.
Sheldon gets upset about his career, the destruction of the comic book store and Leonard and Penny's future living arrangements. Howard and Bernadette struggle to keep hold of a caregiver for Mrs. Wolowitz.