Episode 1 | The Bad Fish Paradigm

Leonard becomes concerned when his date with Penny ends abruptly and she starts blowing him off. When told the truth, Sheldon would rather move out than keep Penny's reasons a secret from Leonard.

Episode 2 | The Codpiece Topology

Sheldon is annoyed when Leonard turns to Leslie for comfort after seeing Penny with another guy.

Episode 3 | The Barbarian Sublimation

Sheldon introduces Penny to online gaming, however she refuses to quit after becoming addicted.

Episode 4 | The Griffin Equivalency

The guys struggle to cope with Raj's arrogance after he is featured in a People magazine article.

Episode 5 | The Euclid Alternative

Sheldon annoys the gang when Leonard can't drive him to and from work, so they try to teach him how to drive.

Episode 6 | The Cooper-Nowitzki Theorem

Sheldon is flattered when a graduate student takes a shine to him, however her extreme devotion becomes too much to handle.

Episode 7 | The Panty Piñata Polarization

Penny plans revenge when Sheldon bans her from his and Leonard's apartment, while Howard and Raj use the latest technology to try to find the house being used in "America's Next Top Model."

Episode 8 | The Lizard-Spock Expansion

Leonard and Howard's friendship is jeopardised when Leonard steals a girl from Howard.

Episode 9 | The White Asparagus Triangulation

Sheldon believes that Leonard will wreck his relationship with Stephanie, so he decides to take matters into his own hands.

Episode 10 | The Vartabedian Conundrum

Leonard tries to slow down his relationship with Stephanie when he realizes that they are living together, while Sheldon becomes convinced that he has an untraceable disease.

Episode 11 | The Bath Item Gift Hypothesis

Leonard is disappointed when Penny develops an interest in an attractive physicist at the university. Meanwhile, Sheldon struggles to find an appropriate Christmas gift for Penny.

Episode 12 | The Killer Robot Instability

Howard becomes depressed after Penny makes a cruel statement about his love life, while the rest of the guys prepare for a grudge killer robot duel against an obnoxious colleague at the university.

Episode 13 | The Friendship Algorithm

Sheldon tries to make friends with Kripke in the hope that it will get him access to a coveted computer at the university.

Episode 14 | The Financial Permeability

Leonard and Sheldon try to help out Penny when she can't afford to pay her rent.

Episode 15 | The Maternal Capacitance

Sheldon hits it off with Leonard's psychoanalyst mother, but she drives Leonard and Penny to the bottle.

Episode 16 | The Cushion Saturation

Howard hooks up with Leslie, while Penny accidentally ruins Sheldon's spot on the couch.

Episode 17 | The Terminator Decoupling

On a train to San Francisco, Howard, Raj and Leonard fight for the affections of sci-fi star Summer Glau, while Sheldon is forced to turn to Penny for help when he leaves his flash drive behind.

Episode 18 | The Work Song Nanocluster

Sheldon's assistance with Penny's home-based business leads to chaos.

Episode 19 | The Dead Hooker Juxtaposition

Penny becomes jealous when a gorgeous new neighbor attracts the guys' attention.

Episode 20 | The Hofstadter Isotope

Leonard is upset when the owner of the comic book store goes on a date with Penny, so he convinces Howard and Raj to take him to a bar so that he can pick up a woman of his own.

Episode 21 | The Vegas Renormalization

After being dumped by Leslie, Howard heads to Las Vegas with Leonard and Raj. Meanwhile, Penny is forced to take in Sheldon after he locks himself out of his apartment.

Episode 22 | The Classified Materials Turbulence

Penny's second date with Stuart has significant implications for Leonard. Howard enlists the guys' help with one of his NASA projects.

Episode 23 | The Monopolar Expedition

Penny gets upset when she finds out Leonard and the guys plan to work at the North Pole for the summer.