<title>Moja biblioteka

1x1 - Pilot

Brilliant physicist roommates Leonard and Sheldon meet their new neighbor Penny, who begins showing them that as much as they know about science, they know little about actual living.

1x2 - The Big Bran Hypothesis

Leonard volunteers to sign for a package in an attempt to make a good impression on Penny, but when he enlists Sheldon for help, his attempt at chivalry goes terribly awry.

1x3 - The Fuzzy Boots Corollary

Leonard asks a woman out after he finds out that Penny is seeing someone.

1x4 - The Luminous Fish Effect

Sheldon's getting fired forces him to explore what life has to offer outside physics, leaving Leonard to take drastic action to snap his friend out of his funk.

1x5 - The Hamburger Postulate

Fearing he's wasting his time on Penny, Leonard ends up making a connection with Leslie.

1x6 - The Middle Earth Paradigm

Penny hosts a Hallowe'en party, putting Leonard, Sheldon, Wolowitz, and Koothrappali through a new test of their social skills.

1x7 - The Dumpling Paradox

With Wolowitz AWOL with one of her friends, Penny's recruited to fill in for him on the guys' Halo team

1x8 - The Grasshopper Experiment

Raj's parents set him up on a blind date, but just when he discovers he can talk to her, she shows interest in Sheldon.

1x9 - The Cooper-Hofstadter Polarization

When they're invited to present at a physics conference, Sheldon's reluctance to share the credit leads to a tiff between him and Leonard, and Penny's intervention only exacerbates the situation.

1x10 - The Loobenfeld Decay

Leonard and Sheldon each lie to avoid seeing Penny's concert, but Sheldon's is a bit too complicated for his own good.

1x11 - The Pancake Batter Anomaly

With his friends knowing how sour he acts when sick—and avoiding him as a result—Sheldon is nursed by Penny, who hasn't a clue what she's in for.

1x12 - The Jerusalem Duality

With Sheldon rattled over meeting Dennis, a 15-year-old physicist who's smarter than he, Leonard helps him look for a way to debunk Dennis's research.

1x13 - The Bat Jar Conjecture

Sheldon finds himself booted from the gang's Physics Bowl team and replaced with Leslie, so he forms his own team, hoping to prove he's superior.

1x14 - The Nerdvana Annihilation

When delivery of another collectible leads to Penny's lashing out at Leonard, he decides it's time to give up his habit, much to his friends' protestation.

1x15 - The Pork Chop Indeterminacy

The rest of the gang fall for Sheldon's twin sister, and Leonard's plan to win her heart is derailed when Sheldon declares he'll be the one to decide who can date her.

1x16 - The Peanut Reaction

Penny wants to throw a surprise party for Leonard, but Sheldon's indulgence at an electronics store throws her off-track.

1x17 - The Tangerine Factor

Penny's break-up spurs Leonard to summon the courage to ask her out, and each goes to Sheldon for advice on their upcoming date.

2x1 - The Bad Fish Paradigm

Penny's first date with Leonard goes awry; Penny finds Sheldon to be an unwilling confidant.

2x2 - The Codpiece Topology

A jealous Leonard reacts to Penny's new guy by rebounding with Leslie.

2x3 - The Barbarian Sublimation

Sheldon creates a monster when he introduces Penny to online gaming.

2x4 - The Griffin Equivalency

Raj gets an inflated ego and makes a play for Penny after being referenced in a magazine article.

2x5 - The Euclid Alternative

Leonard and his friends stage an intervention to force Sheldon to face his fear of driving.

2x6 - The Cooper-Nowitzki Theorem

Sheldon and the gang are confused when a young grad student is attracted to him.

2x7 - The Panty Piñata Polarization

When Sheldon bans Penny from the apartment for numerous minor infractions, she decides to retaliate.

2x8 - The Lizard-Spock Expansion

Leonard inadvertently steals away the new woman Wolowitz thinks is the love of his life.

2x9 - The White Asparagus Triangulation

Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon's stringent standards.

2x10 - The Vartabedian Conundrum

Leonard asks Penny for advice when his new relationship starts moving too fast.

2x11 - The Bath Item Gift Hypothesis

Penny starts dating Leonard's handsome colleague; Leonard and his friends are tortured by Sheldon's obsession with gift-giving etiquette.

2x12 - The Killer Robot Instability

Penny's criticism of Wolowitz's romantic life pushes him into depression and AWOL for a fighting robot battle the rest of guys are depending on him for.

2x13 - The Friendship Algorithm

Sheldon creates a scientific procedure for making friends.

2x14 - The Financial Permeability

Sheldon's solution to Penny's financial difficulty leads to a confrontation between Leonard and Penny's ex-boyfriend.

2x15 - The Maternal Capacitance

Leonard and Penny are drawn together after a disastrous visit from Leonard's mother.

2x16 - The Cushion Saturation

A paintball game leads to a fight between Sheldon and Penny, and romance for Leslie and Wolowitz.

2x17 - The Terminator Decoupling

Leonard, Sheldon and Wolowitz are ecstatic to learn that a famous science-fiction actress (Summer Glau) is on board the train they are taking to San Francisco.

2x18 - The Work Song Nanocluster

Penny's home business turns into a complete nightmare when Sheldon takes over.

2x19 - The Dead Hooker Juxtaposition

Penny squares off with a new beautiful female neighbor who may become the building's "new Penny."

2x20 - The Hofstadter Isotope

A fellow comic book enthusiast's hitting on Penny leads to Leonard and Howard going to a bar's Ladies' Night.

2x21 - The Vegas Renormalization

Leonard and Koothrappali escort a heartbroken Wolowitz to Las Vegas, and Sheldon becomes locked out of his apartment and must stay with Penny.

2x22 - The Classified Materials Turbulence

Penny's second date with Stuart sees her making a comment that gives Leonard new hope for a relationship with her. Wolowitz realizes there's a crucial error in a NASA project he's working on.

2x23 - The Monopolar Expedition

The guys' plan to work over the summer at the North Pole makes Penny revaluate her feelings for Leonard.

3x1 - The Electric Can Opener Fluctuation

When Sheldon learns the guys tampered with his expedition data he got from the arctic, he leaves to Texas in disgrace. This results in the guys following him, which threatens Leonard's hope for some romantic time with Penny and the guys' friendship with Sheldon.

3x2 - The Jiminy Conjecture

Leonard and Penny struggle to recover from an awkward first hookup while Sheldon and Howard stake their best comic books on a bet to determine the species of a cricket.

3x3 - The Gothowitz Deviation

Howard and Raj visit a Goth nightclub to pick up women while Sheldon attempts to build a better Penny using chocolate-based behavior modification.

3x4 - The Pirate Solution

Raj must find a new job or be sent back to India, but Sheldon has a solution, which leaves Leonard and Penny dealing with Howard as a third wheel.

3x5 - The Creepy Candy Coating Corollary

After overhearing that Wil Wheaton is entering a trading-card competition, Sheldon decides to enter it himself. Meanwhile, Penny sets up one of her friends on a date with Wolowitz.

3x6 - The Cornhusker Vortex

Sheldon becomes Leonard's teacher in order to understand football, while an incident with flying a kite threatens Howard and Raj's friendship.

3x7 - The Guitarist Amplification

A squabble between Leonard and Penny sees Sheldon playing mediator, though out of his own incovenience from the sitiation rather than altruism.

3x8 - The Adhesive Duck Deficiency

With Leonard, Howard and Raj away camping in the desert, an injured Penny has only Sheldon to rely on.

3x9 - The Vengeance Formulation

After he's humiliated on National Public Radio, Sheldon vows to destroy Kripke, while Wolowitz tries not to destroy his new relationship with Bernadette.

3x10 - The Gorilla Experiment

Penny gets help from Sheldon in order to understand what Leonard's work is, while Wolowitz develops a jealousy when Leonard starts hanging out with his new girlfriend.

3x11 - The Maternal Congruence

A Christmas visit from his mother has Leonard discovering she's kept a lot of news from him that she shares with Sheldon and worrying if she'll approve of his romance with Penny.

3x12 - The Psychic Vortex

Leonard is aghast to find out a secret of Penny's: she believes in psychics. Meanwhile, Sheldon tries to assist Koothrappali in picking up a girl at a university mixer.

3x13 - The Bozeman Reaction

When their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.

3x14 - The Einstein Approximation

Sheldon's search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.

3x15 - The Large Hadron Collision

Leonard can only bring one guest on a trip to see CERN's Large Hadron Collider (the world's largest and highest energy particle accelerator) in Switzerland on Valentine's Day.

3x16 - The Excelsior Acquisition

Sheldon winds up in traffic court when he gets a ticket because of Penny.

3x17 - The Precious Fragmentation

When the guys find a ring from "The Lord of the Rings" at a garage sale, it threatens to tear them apart.

3x18 - The Pants Alternative

Sheldon's friends come to his aid when his fear of public speaking stands between him and a coveted award.

3x19 - The Wheaton Recurrence

A fight between Leonard and Penny threatens their relationship, while Sheldon battles Wil Wheaton in bowling.

3x20 - The Spaghetti Catalyst

When Leonard and Penny aren't speaking, Sheldon goes to extremes to keep them both happy.

3x21 - The Plimpton Stimulation

Leonard and Sheldon compete for the attention of a famous female physicist.

3x22 - The Staircase Implementation

Leonard tells Penny about how he met Sheldon for the first time...and what happened to the elevator.

3x23 - The Lunar Excitation

While Penny worries that dating Leonard has ruined her for normal guys, Wolowitz and Koothrappali search for Sheldon's perfect match online.

5x1 - The Skank Reflex Analysis

Penny is worried with how damaged her friendship with the guys will be in the aftermath of her sleeping with Raj while Sheldon becomes the leader of the paintball team.

5x2 - The Infestation Hypothesis

A fight between Sheldon and Penny leaves Amy caught in the middle, while Leonard tries to spice up his long-distance relationship with Priya.

5x3 - The Pulled Groin Extrapolation

Leonard and Amy get to know each other better, while Howard and Bernadette spend the weekend with Mrs. Wolowitz.

5x4 - The Wiggly Finger Catalyst

Penny plays Matchmaker for Raj, which results in him finding a girl he is comfortable talking to.

5x5 - The Russian Rocket Reaction

Sheldon and Leonard get invited to a party at Wil Wheaton's house, and Howard gets an out-of-this-world opportunity.

5x6 - The Rhinitis Revelation

Sheldon's mother, Mary Cooper, comes to visit, but Sheldon is annoyed that she also spends time with the rest of the gang, instead of catering to his every demand.

5x7 - The Good Guy Fluctuation

A cute comic book artist puts Leonard and Priya’s relationship to the test, while Sheldon tries to scare the guys for Halloween.

5x8 - The Isolation Permutation

Amy becomes heartbroken when she discovers that Penny and Bernadette went wedding dress shopping without her.

5x10 - The Flaming Spittoon Acquisition

Sheldon considers taking his relationship with Amy to the next level when Stuart from the comic book store asks her out on a date.

5x11 - The Speckerman Recurrence

Leonard must face his fears after being contacted by his high school tormentor.

5x12 - The Shiny Trinket Maneuver

Sheldon gets in trouble with Amy when he isn't impressed by her recent accomplishment, and Howard must come to grips with Bernadette's dislike of children.

5x13 - The Recombination Hypothesis

Leonard, who broke up with Priya, asks Penny out to a spur-of the-moment romantic dinner for two, and the duo contemplates on their relationship.

5x14 - The Beta Test Initiation

Leonard and Penny deal with the idea of starting a relationship again and Raj finally finds a "woman" he can talk to without being drunk, in the form of Siri on his new phone. Meanwhile, Sheldon decides to start a YouTube series entitled "Sheldon Cooper presents Fun with Flags" with the help of Amy.

5x15 - The Friendship Contraction

Sheldon's selfish demands force Leonard to reconsider their friendship. Meanwhile, Wolowitz tries to pick his astronaut nickname.

5x16 - The Vacation Solution

When Sheldon is forced to take his vacation, he goes to work with Amy in her neurobiology lab.

5x17 - The Rothman Disintegration

Penny is horrified when Amy gives her a gift: a huge, quite horrible painting of the two of them. With no good way to avoid displaying it, she only hangs it up when Amy is over. When Amy catches her taking the painting down, she's embarrassed and angry until Penny lies and says the gift made Bernadette jealous. When the deranged Professor Rothman is forced to retire, both Sheldon and Kripke vie for his office. President Siebert refuses to resolve the dispute, so Leonard arranges a one-on-one basketball game to decide (since they're both equally bad at sports). Neither one can even make a single basket, so they end up deciding by seeing who can bounce the ball the highest. Sheldon wins; unfortunately, the office is not what he'd hoped for: the thermostat is located in the office of a professor going through the hot flashes of menopause (thus Sheldon is too cold), the mockingbird outside his window is off-key with the annoying windchimes, the perpetually naked Professor Rothman refuses to vacate, and the Geology Department upstairs makes too much noise. Finally, Sheldon gets his head stuck in the wall in an existing hole, after which Leonard takes his picture before he goes for help.

5x18 - The Werewolf Transformation

Sheldon becomes agitated when his regular barber is out sick. Astronaut training causes Howard to reconsider wanting to go into space. Penny beats Leonard in chess, the first time she plays.

5x19 - The Weekend Vortex

Sheldon must choose between joining Amy at her aunt's birthday party or playing videogames all weekend with the guys.

5x20 - The Transporter Malfunction

Penny buys Leonard and Sheldon “Star Trek” collectibles as a thank-you, leading Sheldon to be haunted by Mr. Spock. Meanwhile, Raj decides he has met the “Future Mrs. Koothrappali” after his parents set him up on a date.

5x21 - The Hawking Excitation

When Wolowitz gets to work with Stephen Hawking, Sheldon is willing to do anything to meet his hero.

5x22 - The Stag Convergence

After the guys throw Howard a bachelor party, Bernadette reconsiders marrying him after learning about his sexual history.

5x23 - The Launch Acceleration

When NASA moves up Howard's mission, he must face his fears and Bernadette's dad, thus putting the wedding plans in jeopardy. Meanwhile, Leonard says something surprising to Penny in the bedroom.

5x24 - The Countdown Reflection

The fifth season ends with Howard and Bernadette deciding to get married before his NASA mission, causing the gang to scurry into overdrive in an effort to stage the wedding. NASA astronaut Mike Massimino has a cameo as himself.

6x1 - The Date Night Variable

Raj faces his loneliness when his friends are out on dates; while in space, Wolowitz gets drawn into a fight between Bernadette and his mom.

6x2 - The Decoupling Fluctuation

Sheldon tries to intervene when he learns that Penny is thinking about breaking up with Leonard; Howard is picked on.

6x3 - The Higgs Boson Observation

Amy feels threatened by Sheldon's new assistant; Wolowitz starts to feel the pressures of being in space.

6x4 - The Re-Entry Minimization

Wolowitz's return from space isn't all he expected; game night becomes a gender war.

6x5 - The Holographic Excitation

The gang heads to Stuart's comic book store to celebrate Halloween; Leonard uses science to seduce Penny.

6x6 - The Extract Obliteration

A game threatens Sheldon's relationship with Stephen Hawking; Penny secretly signs up for a college class.

6x7 - The Habitation Configuration

Bernadette wants Wolowitz to move out of his mom's house; Sheldon is caught in the middle of Amy and Wil Wheaton's argument.

6x8 - The 43 Peculiarity

Raj and Howard try to to figure out why Sheldon disappears at 2:45 every afternoon; jealousy arises in Penny and Leonard's relationship.

6x9 - The Parking Spot Escalation

Sheldon and Wolowitz's fight over a parking spot at the university impacts the whole gang.

6x10 - The Fish Guts Displacement

When Amy gets sick, Sheldon tries to nurse her back to health; Wolowitz and his father-in-law plan a fishing trip.

6x11 - The Santa Simulation

During a game, Sheldon revisits Christmas memories; Amy, Penny and Bernadette look for a date for Koothrappali.

6x12 - The Egg Salad Equivalency

When Sheldon is accused of sexual harassment, he ends up getting Raj, Leonard and Wolowitz in trouble.

6x13 - The Bakersfield Expedition

As the guys don costumes and go on a road trip to a comic book convention, the ladies decide to stay home and try to interpret a comic book.

6x14 - The Cooper/Kripke Inversion

Sheldon faces a crisis of confidence when he is forced to work with his nemesis, Barry Kripke; Raj and Howard buy expensive action figures of themselves.

6x15 - The Spoiler Alert Segmentation

A fight between Sheldon and Leonard impacts Amy and Penny's living arrangements; while Howard is away, Raj helps Mrs. Wolowitz out.

6x16 - The Tangible Affection Proof

The guys search for a perfect Valentine's Day gift for their significant others; Stuart and Raj host a "lonely people" party at the comic book store.

6x17 - The Monster Isolation

After a bad date, Koothrappali decides to never leave his apartment; Penny's acting skills impress Sheldon.

6x18 - The Contractual Obligation Implementation

Leonard, Sheldon and Wolowitz talk to junior high girls about science-related careers; Raj plans a date with Lucy.

6x19 - The Closet Reconfiguration

Howard considers whether or not he should open a letter from his father; Penny and Leonard host a "grown-up" cocktail party.

6x20 - The Tenure Turbulence

The girls get involved when Leonard, Sheldon and Raj compete for tenure at the University.

6x21 - The Closure Alternative

Amy tries to help Sheldon get over his compulsive need for closure when one of his favorite TV shows is canceled; Raj discovers a secret about Lucy.

6x22 - The Proton Resurgence

Leonard and Sheldon hire the host (Bob Newhart) of their favorite childhood TV show to perform; Bernadette and Howard run into trouble while dog-sitting for Raj's pet.

6x23 - The Love Spell Potential

Amy and Sheldon's relationship takes a surprising turn during a game of "Dungeons & Dragons"; Lucy and Koothrappali have an awkward date.

6x24 - The Bon Voyage Reaction

When Leonard is considered for an exciting research opportunity, Sheldon becomes jealous and tries to scare him into backing out. Meanwhile, Raj's relationship with Lucy is strained when he tries to get her to meet his friends.

7x1 - The Hofstadter Insufficiency

Sheldon and Penny share secrets while Leonard is away; Wolowitz helps Raj get over his ex.

7x2 - The Deception Verification

Leonard and Sheldon's friendship is tested; Wolowitz's relationship with his mom causes a threat to his masculinity.

7x3 - The Scavenger Vortex

Raj designs a scavenger hunt that brings out the best -- and the worst -- in the whole gang.

7x4 - The Raiders Minimization

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.

7x5 - The Workplace Proximity

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.

7x6 - The Romance Resonance

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.

7x7 - The Proton Displacement

When Professor Proton asks Leonard for help with an experiment, Sheldon retaliates by befriending Proton's rival, Bill Nye.

7x8 - The Itchy Brain Simulation

When a mistake comes to light, Sheldon makes Leonard walk a mile in his shoes; Penny decides to confront Raj's ex.

7x9 - The Thanksgiving Decoupling

When the gang decides to spend Thanksgiving at Mrs. Wolowitz's house, Sheldon protests; Leonard and Penny deal with an error from her past.

7x10 - The Discovery Dissipation

Amy and Leonard try to help Sheldon deal with his shame; Raj stays with Bernadette and Howard for a week.

7x11 - The Cooper Extraction

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.

7x12 - The Hesitation Ramification

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.

7x18 - The Mommy Observation

Sheldon is faced with a new reality when he visits his mom in Houston; a murder mystery party starts arguments.

7x19 - The Indecision Amalgamation

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.

7x20 - The Relationship Diremption

Sheldon has a personal crisis when he decides string theory is a waste of his time; a double date ends in embarrassment for Howard.

7x21 - The Anything Can Happen Recurrence

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.

7x22 - The Proton Transmogrification

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.

7x23 - The Gorilla Dissolution

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.

7x24 - The Status Quo Combustion

Faced with an uncertain future, Sheldon considers a major change; Emily and Raj decide to take things to the next level.

1x1 - Pilot

Brilliant physicist roommates Leonard and Sheldon meet their new neighbor Penny, who begins showing them that as much as they know about science, they know little about actual living.

1x2 - The Big Bran Hypothesis

Leonard volunteers to sign for a package in an attempt to make a good impression on Penny, but when he enlists Sheldon for help, his attempt at chivalry goes terribly awry.

1x3 - The Fuzzy Boots Corollary

Leonard asks a woman out after he finds out that Penny is seeing someone.

1x4 - The Luminous Fish Effect

Sheldon's getting fired forces him to explore what life has to offer outside physics, leaving Leonard to take drastic action to snap his friend out of his funk.

1x5 - The Hamburger Postulate

Fearing he's wasting his time on Penny, Leonard ends up making a connection with Leslie.

1x6 - The Middle Earth Paradigm

Penny hosts a Hallowe'en party, putting Leonard, Sheldon, Wolowitz, and Koothrappali through a new test of their social skills.

1x7 - The Dumpling Paradox

With Wolowitz AWOL with one of her friends, Penny's recruited to fill in for him on the guys' Halo team

1x8 - The Grasshopper Experiment

Raj's parents set him up on a blind date, but just when he discovers he can talk to her, she shows interest in Sheldon.

1x9 - The Cooper-Hofstadter Polarization

When they're invited to present at a physics conference, Sheldon's reluctance to share the credit leads to a tiff between him and Leonard, and Penny's intervention only exacerbates the situation.

1x10 - The Loobenfeld Decay

Leonard and Sheldon each lie to avoid seeing Penny's concert, but Sheldon's is a bit too complicated for his own good.

1x11 - The Pancake Batter Anomaly

With his friends knowing how sour he acts when sick—and avoiding him as a result—Sheldon is nursed by Penny, who hasn't a clue what she's in for.

1x12 - The Jerusalem Duality

With Sheldon rattled over meeting Dennis, a 15-year-old physicist who's smarter than he, Leonard helps him look for a way to debunk Dennis's research.

1x13 - The Bat Jar Conjecture

Sheldon finds himself booted from the gang's Physics Bowl team and replaced with Leslie, so he forms his own team, hoping to prove he's superior.

1x14 - The Nerdvana Annihilation

When delivery of another collectible leads to Penny's lashing out at Leonard, he decides it's time to give up his habit, much to his friends' protestation.

1x15 - The Pork Chop Indeterminacy

The rest of the gang fall for Sheldon's twin sister, and Leonard's plan to win her heart is derailed when Sheldon declares he'll be the one to decide who can date her.

1x16 - The Peanut Reaction

Penny wants to throw a surprise party for Leonard, but Sheldon's indulgence at an electronics store throws her off-track.

1x17 - The Tangerine Factor

Penny's break-up spurs Leonard to summon the courage to ask her out, and each goes to Sheldon for advice on their upcoming date.

2x1 - The Bad Fish Paradigm

Penny's first date with Leonard goes awry; Penny finds Sheldon to be an unwilling confidant.

2x2 - The Codpiece Topology

A jealous Leonard reacts to Penny's new guy by rebounding with Leslie.

2x3 - The Barbarian Sublimation

Sheldon creates a monster when he introduces Penny to online gaming.

2x4 - The Griffin Equivalency

Raj gets an inflated ego and makes a play for Penny after being referenced in a magazine article.

2x5 - The Euclid Alternative

Leonard and his friends stage an intervention to force Sheldon to face his fear of driving.

2x6 - The Cooper-Nowitzki Theorem

Sheldon and the gang are confused when a young grad student is attracted to him.

2x7 - The Panty Piñata Polarization

When Sheldon bans Penny from the apartment for numerous minor infractions, she decides to retaliate.

2x8 - The Lizard-Spock Expansion

Leonard inadvertently steals away the new woman Wolowitz thinks is the love of his life.

2x9 - The White Asparagus Triangulation

Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon's stringent standards.

2x10 - The Vartabedian Conundrum

Leonard asks Penny for advice when his new relationship starts moving too fast.

2x11 - The Bath Item Gift Hypothesis

Penny starts dating Leonard's handsome colleague; Leonard and his friends are tortured by Sheldon's obsession with gift-giving etiquette.

2x12 - The Killer Robot Instability

Penny's criticism of Wolowitz's romantic life pushes him into depression and AWOL for a fighting robot battle the rest of guys are depending on him for.

2x13 - The Friendship Algorithm

Sheldon creates a scientific procedure for making friends.

2x14 - The Financial Permeability

Sheldon's solution to Penny's financial difficulty leads to a confrontation between Leonard and Penny's ex-boyfriend.

2x15 - The Maternal Capacitance

Leonard and Penny are drawn together after a disastrous visit from Leonard's mother.

2x16 - The Cushion Saturation

A paintball game leads to a fight between Sheldon and Penny, and romance for Leslie and Wolowitz.

2x17 - The Terminator Decoupling

Leonard, Sheldon and Wolowitz are ecstatic to learn that a famous science-fiction actress (Summer Glau) is on board the train they are taking to San Francisco.

2x18 - The Work Song Nanocluster

Penny's home business turns into a complete nightmare when Sheldon takes over.

2x19 - The Dead Hooker Juxtaposition

Penny squares off with a new beautiful female neighbor who may become the building's "new Penny."

2x20 - The Hofstadter Isotope

A fellow comic book enthusiast's hitting on Penny leads to Leonard and Howard going to a bar's Ladies' Night.

2x21 - The Vegas Renormalization

Leonard and Koothrappali escort a heartbroken Wolowitz to Las Vegas, and Sheldon becomes locked out of his apartment and must stay with Penny.

2x22 - The Classified Materials Turbulence

Penny's second date with Stuart sees her making a comment that gives Leonard new hope for a relationship with her. Wolowitz realizes there's a crucial error in a NASA project he's working on.

2x23 - The Monopolar Expedition

The guys' plan to work over the summer at the North Pole makes Penny revaluate her feelings for Leonard.

3x1 - The Electric Can Opener Fluctuation

When Sheldon learns the guys tampered with his expedition data he got from the arctic, he leaves to Texas in disgrace. This results in the guys following him, which threatens Leonard's hope for some romantic time with Penny and the guys' friendship with Sheldon.

3x2 - The Jiminy Conjecture

Leonard and Penny struggle to recover from an awkward first hookup while Sheldon and Howard stake their best comic books on a bet to determine the species of a cricket.

3x3 - The Gothowitz Deviation

Howard and Raj visit a Goth nightclub to pick up women while Sheldon attempts to build a better Penny using chocolate-based behavior modification.

3x4 - The Pirate Solution

Raj must find a new job or be sent back to India, but Sheldon has a solution, which leaves Leonard and Penny dealing with Howard as a third wheel.

3x5 - The Creepy Candy Coating Corollary

After overhearing that Wil Wheaton is entering a trading-card competition, Sheldon decides to enter it himself. Meanwhile, Penny sets up one of her friends on a date with Wolowitz.

3x6 - The Cornhusker Vortex

Sheldon becomes Leonard's teacher in order to understand football, while an incident with flying a kite threatens Howard and Raj's friendship.

3x7 - The Guitarist Amplification

A squabble between Leonard and Penny sees Sheldon playing mediator, though out of his own incovenience from the sitiation rather than altruism.

3x8 - The Adhesive Duck Deficiency

With Leonard, Howard and Raj away camping in the desert, an injured Penny has only Sheldon to rely on.

3x9 - The Vengeance Formulation

After he's humiliated on National Public Radio, Sheldon vows to destroy Kripke, while Wolowitz tries not to destroy his new relationship with Bernadette.

3x10 - The Gorilla Experiment

Penny gets help from Sheldon in order to understand what Leonard's work is, while Wolowitz develops a jealousy when Leonard starts hanging out with his new girlfriend.

3x11 - The Maternal Congruence

A Christmas visit from his mother has Leonard discovering she's kept a lot of news from him that she shares with Sheldon and worrying if she'll approve of his romance with Penny.

3x12 - The Psychic Vortex

Leonard is aghast to find out a secret of Penny's: she believes in psychics. Meanwhile, Sheldon tries to assist Koothrappali in picking up a girl at a university mixer.

3x13 - The Bozeman Reaction

When their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.

3x14 - The Einstein Approximation

Sheldon's search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.

3x15 - The Large Hadron Collision

Leonard can only bring one guest on a trip to see CERN's Large Hadron Collider (the world's largest and highest energy particle accelerator) in Switzerland on Valentine's Day.

3x16 - The Excelsior Acquisition

Sheldon winds up in traffic court when he gets a ticket because of Penny.

3x17 - The Precious Fragmentation

When the guys find a ring from "The Lord of the Rings" at a garage sale, it threatens to tear them apart.

3x18 - The Pants Alternative

Sheldon's friends come to his aid when his fear of public speaking stands between him and a coveted award.

3x19 - The Wheaton Recurrence

A fight between Leonard and Penny threatens their relationship, while Sheldon battles Wil Wheaton in bowling.

3x20 - The Spaghetti Catalyst

When Leonard and Penny aren't speaking, Sheldon goes to extremes to keep them both happy.

3x21 - The Plimpton Stimulation

Leonard and Sheldon compete for the attention of a famous female physicist.

3x22 - The Staircase Implementation

Leonard tells Penny about how he met Sheldon for the first time...and what happened to the elevator.

3x23 - The Lunar Excitation

While Penny worries that dating Leonard has ruined her for normal guys, Wolowitz and Koothrappali search for Sheldon's perfect match online.

5x1 - The Skank Reflex Analysis

Penny is worried with how damaged her friendship with the guys will be in the aftermath of her sleeping with Raj while Sheldon becomes the leader of the paintball team.

5x2 - The Infestation Hypothesis

A fight between Sheldon and Penny leaves Amy caught in the middle, while Leonard tries to spice up his long-distance relationship with Priya.

5x3 - The Pulled Groin Extrapolation

Leonard and Amy get to know each other better, while Howard and Bernadette spend the weekend with Mrs. Wolowitz.

5x4 - The Wiggly Finger Catalyst

Penny plays Matchmaker for Raj, which results in him finding a girl he is comfortable talking to.

5x5 - The Russian Rocket Reaction

Sheldon and Leonard get invited to a party at Wil Wheaton's house, and Howard gets an out-of-this-world opportunity.

5x6 - The Rhinitis Revelation

Sheldon's mother, Mary Cooper, comes to visit, but Sheldon is annoyed that she also spends time with the rest of the gang, instead of catering to his every demand.

5x7 - The Good Guy Fluctuation

A cute comic book artist puts Leonard and Priya’s relationship to the test, while Sheldon tries to scare the guys for Halloween.

5x8 - The Isolation Permutation

Amy becomes heartbroken when she discovers that Penny and Bernadette went wedding dress shopping without her.

5x9 - The Ornithophobia Diffusion

Leonard and Penny try hanging out as friends on a 'non-date', but end up purposely ruining each others chances with perspective dates. Meanwhile, Sheldon enlists the help of Bernadette and Amy to overcome his fear of birds.

5x10 - The Flaming Spittoon Acquisition

Sheldon considers taking his relationship with Amy to the next level when Stuart from the comic book store asks her out on a date.

5x11 - The Speckerman Recurrence

Leonard must face his fears after being contacted by his high school tormentor.

5x12 - The Shiny Trinket Maneuver

Sheldon gets in trouble with Amy when he isn't impressed by her recent accomplishment, and Howard must come to grips with Bernadette's dislike of children.

5x13 - The Recombination Hypothesis

Leonard, who broke up with Priya, asks Penny out to a spur-of the-moment romantic dinner for two, and the duo contemplates on their relationship.

5x14 - The Beta Test Initiation

Leonard and Penny deal with the idea of starting a relationship again and Raj finally finds a "woman" he can talk to without being drunk, in the form of Siri on his new phone. Meanwhile, Sheldon decides to start a YouTube series entitled "Sheldon Cooper presents Fun with Flags" with the help of Amy.

5x15 - The Friendship Contraction

Sheldon's selfish demands force Leonard to reconsider their friendship. Meanwhile, Wolowitz tries to pick his astronaut nickname.

5x16 - The Vacation Solution

When Sheldon is forced to take his vacation, he goes to work with Amy in her neurobiology lab.

5x17 - The Rothman Disintegration

Penny is horrified when Amy gives her a gift: a huge, quite horrible painting of the two of them. With no good way to avoid displaying it, she only hangs it up when Amy is over. When Amy catches her taking the painting down, she's embarrassed and angry until Penny lies and says the gift made Bernadette jealous. When the deranged Professor Rothman is forced to retire, both Sheldon and Kripke vie for his office. President Siebert refuses to resolve the dispute, so Leonard arranges a one-on-one basketball game to decide (since they're both equally bad at sports). Neither one can even make a single basket, so they end up deciding by seeing who can bounce the ball the highest. Sheldon wins; unfortunately, the office is not what he'd hoped for: the thermostat is located in the office of a professor going through the hot flashes of menopause (thus Sheldon is too cold), the mockingbird outside his window is off-key with the annoying windchimes, the perpetually naked Professor Rothman refuses to vacate, and the Geology Department upstairs makes too much noise. Finally, Sheldon gets his head stuck in the wall in an existing hole, after which Leonard takes his picture before he goes for help.

5x18 - The Werewolf Transformation

Sheldon becomes agitated when his regular barber is out sick. Astronaut training causes Howard to reconsider wanting to go into space. Penny beats Leonard in chess, the first time she plays.

5x19 - The Weekend Vortex

Sheldon must choose between joining Amy at her aunt's birthday party or playing videogames all weekend with the guys.

5x20 - The Transporter Malfunction

Penny buys Leonard and Sheldon “Star Trek” collectibles as a thank-you, leading Sheldon to be haunted by Mr. Spock. Meanwhile, Raj decides he has met the “Future Mrs. Koothrappali” after his parents set him up on a date.

5x21 - The Hawking Excitation

When Wolowitz gets to work with Stephen Hawking, Sheldon is willing to do anything to meet his hero.

5x22 - The Stag Convergence

After the guys throw Howard a bachelor party, Bernadette reconsiders marrying him after learning about his sexual history.

5x23 - The Launch Acceleration

When NASA moves up Howard's mission, he must face his fears and Bernadette's dad, thus putting the wedding plans in jeopardy. Meanwhile, Leonard says something surprising to Penny in the bedroom.

5x24 - The Countdown Reflection

The fifth season ends with Howard and Bernadette deciding to get married before his NASA mission, causing the gang to scurry into overdrive in an effort to stage the wedding. NASA astronaut Mike Massimino has a cameo as himself.

6x1 - The Date Night Variable

Raj faces his loneliness when his friends are out on dates; while in space, Wolowitz gets drawn into a fight between Bernadette and his mom.

6x2 - The Decoupling Fluctuation

Sheldon tries to intervene when he learns that Penny is thinking about breaking up with Leonard; Howard is picked on.

6x3 - The Higgs Boson Observation

Amy feels threatened by Sheldon's new assistant; Wolowitz starts to feel the pressures of being in space.

6x4 - The Re-Entry Minimization

Wolowitz's return from space isn't all he expected; game night becomes a gender war.

6x5 - The Holographic Excitation

The gang heads to Stuart's comic book store to celebrate Halloween; Leonard uses science to seduce Penny.

6x6 - The Extract Obliteration

A game threatens Sheldon's relationship with Stephen Hawking; Penny secretly signs up for a college class.

6x7 - The Habitation Configuration

Bernadette wants Wolowitz to move out of his mom's house; Sheldon is caught in the middle of Amy and Wil Wheaton's argument.

6x8 - The 43 Peculiarity

Raj and Howard try to to figure out why Sheldon disappears at 2:45 every afternoon; jealousy arises in Penny and Leonard's relationship.

6x9 - The Parking Spot Escalation

Sheldon and Wolowitz's fight over a parking spot at the university impacts the whole gang.

6x10 - The Fish Guts Displacement

When Amy gets sick, Sheldon tries to nurse her back to health; Wolowitz and his father-in-law plan a fishing trip.

6x11 - The Santa Simulation

During a game, Sheldon revisits Christmas memories; Amy, Penny and Bernadette look for a date for Koothrappali.

6x12 - The Egg Salad Equivalency

When Sheldon is accused of sexual harassment, he ends up getting Raj, Leonard and Wolowitz in trouble.

6x13 - The Bakersfield Expedition

As the guys don costumes and go on a road trip to a comic book convention, the ladies decide to stay home and try to interpret a comic book.

6x14 - The Cooper/Kripke Inversion

Sheldon faces a crisis of confidence when he is forced to work with his nemesis, Barry Kripke; Raj and Howard buy expensive action figures of themselves.

6x15 - The Spoiler Alert Segmentation

A fight between Sheldon and Leonard impacts Amy and Penny's living arrangements; while Howard is away, Raj helps Mrs. Wolowitz out.

6x16 - The Tangible Affection Proof

The guys search for a perfect Valentine's Day gift for their significant others; Stuart and Raj host a "lonely people" party at the comic book store.

6x17 - The Monster Isolation

After a bad date, Koothrappali decides to never leave his apartment; Penny's acting skills impress Sheldon.

6x18 - The Contractual Obligation Implementation

Leonard, Sheldon and Wolowitz talk to junior high girls about science-related careers; Raj plans a date with Lucy.

6x19 - The Closet Reconfiguration

Howard considers whether or not he should open a letter from his father; Penny and Leonard host a "grown-up" cocktail party.

6x20 - The Tenure Turbulence

The girls get involved when Leonard, Sheldon and Raj compete for tenure at the University.

6x21 - The Closure Alternative

Amy tries to help Sheldon get over his compulsive need for closure when one of his favorite TV shows is canceled; Raj discovers a secret about Lucy.

6x22 - The Proton Resurgence

Leonard and Sheldon hire the host (Bob Newhart) of their favorite childhood TV show to perform; Bernadette and Howard run into trouble while dog-sitting for Raj's pet.

6x23 - The Love Spell Potential

Amy and Sheldon's relationship takes a surprising turn during a game of "Dungeons & Dragons"; Lucy and Koothrappali have an awkward date.

6x24 - The Bon Voyage Reaction

When Leonard is considered for an exciting research opportunity, Sheldon becomes jealous and tries to scare him into backing out. Meanwhile, Raj's relationship with Lucy is strained when he tries to get her to meet his friends.

7x1 - The Hofstadter Insufficiency

In the first part of the one-hour seventh season premiere, Sheldon and Penny bond in Leonard's absence, but it's Sheldon's feelings that are crushed when Leonard returns from the North Sea. Guest star Regina King returns as Mrs. Davis, the University's Director of Employee Relations.

7x2 - The Deception Verification

On the second part of the one-hour seventh season premiere, Raj gets consoled about his ex-girlfriend and Howard's relationship with his mother causes an unusual threat to his masculinity. Kevin Sussman returns as Stuart, the comic book store owner.

7x3 - The Scavenger Vortex

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.

7x4 - The Raiders Minimization

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.

7x5 - The Workplace Proximity

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.

7x6 - The Romance Resonance

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.

7x7 - The Proton Displacement

Sheldon feels slighted when Professor Proton (recurring guest star Bob Newhart) seeks advice from Leonard instead of him, and he seeks revenge by befriending a rival science TV host, Bill Nye (guest starring as himself). Meanwhile, Raj gets jealous when Howard crashes "girls' night."

7x8 - The Itchy Brain Simulation

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 (guest star Kate Micucci).

7x9 - The Thanksgiving Decoupling

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.

7x10 - The Discovery Dissipation

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

7x11 - The Cooper Extraction

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.

7x12 - The Hesitation Ramification

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.

7x13 - The Occupation Recalibration

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.

7x14 - The Convention Conundrum

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.

7x15 - The Locomotive Manipulation

Sheldon and Amy go on a trip to wine country with Howard and Bernadette; Penny and Leonard rush Raj's dog to the vet

7x16 - The Table Polarization

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.

7x17 - The Friendship Turbulence

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.

4x1 - The Robotic Manipulation

Penny tags along on Sheldon's first ever date; Wolowitz finds a new use for a robotic arm.

4x2 - The Cruciferous Vegetable Amplification

Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.

4x3 - The Zazzy Substitution

The guys are concerned as Sheldon searches for an alternative to human companionship.

4x4 - The Hot Troll Deviation

An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work.

4x5 - The Desperation Emanation

Leonard realizes he’s the only one without a girlfriend, while Sheldon wants to get rid of his.

4x6 - The Irish Pub Formulation

Leonard keeps an affair a secret from Sheldon, Howard and Raj.

4x7 - The Apology Insufficiency

Sheldon's answers during an FBI interview put Wolowitz's security clearance in jeopardy.

7x18 - The Mommy Observation

Sheldon is faced with a new reality when he visits his mom in Houston; a murder mystery party starts arguments.

7x19 - The Indecision Amalgamation

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.

7x20 - The Relationship Diremption

Sheldon has a personal crisis when he decides string theory is a waste of his time; a double date ends in embarrassment for Howard.

7x21 - The Anything Can Happen Recurrence

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.

7x22 - The Proton Transmogrification

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.

7x1 - The Hofstadter Insufficiency

In the first part of the one-hour seventh season premiere, Sheldon and Penny bond in Leonard's absence, but it's Sheldon's feelings that are crushed when Leonard returns from the North Sea. Guest star Regina King returns as Mrs. Davis, the University's Director of Employee Relations.

7x2 - The Deception Verification

On the second part of the one-hour seventh season premiere, Raj gets consoled about his ex-girlfriend and Howard's relationship with his mother causes an unusual threat to his masculinity. Kevin Sussman returns as Stuart, the comic book store owner.

7x3 - The Scavenger Vortex

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.

7x4 - The Raiders Minimization

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.

7x5 - The Workplace Proximity

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.

7x6 - The Romance Resonance

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.

7x7 - The Proton Displacement

Sheldon feels slighted when Professor Proton (recurring guest star Bob Newhart) seeks advice from Leonard instead of him, and he seeks revenge by befriending a rival science TV host, Bill Nye (guest starring as himself). Meanwhile, Raj gets jealous when Howard crashes "girls' night."

7x8 - The Itchy Brain Simulation

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 (guest star Kate Micucci).

7x9 - The Thanksgiving Decoupling

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.

7x10 - The Discovery Dissipation

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

7x11 - The Cooper Extraction

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.

7x12 - The Hesitation Ramification

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.

7x13 - The Occupation Recalibration

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.

7x14 - The Convention Conundrum

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.

7x15 - The Locomotive Manipulation

Sheldon and Amy go on a trip to wine country with Howard and Bernadette; Penny and Leonard rush Raj's dog to the vet

7x16 - The Table Polarization

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.

7x17 - The Friendship Turbulence

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.

7x23 - The Gorilla Dissolution

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.

7x24 - The Status Quo Combustion

Faced with an uncertain future, Sheldon considers a major change; Emily and Raj decide to take things to the next level.

8x1 - The Locomotion Interruption

Leonard and Amy make an unexpected trip to Arizona to fetch Sheldon; Penny interviews for a job at Bernadette's company; Stuart's relationship with Mrs. Wolowitz disturbs Howard.

8x2 - The Junior Professor Solution

When Sheldon must teach a class, Howard decides to take it; Amy takes advantage of the tension between Penny and Bernadette.

4x8 - The 21-Second Excitation

While the guys camp in line for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.

4x9 - The Boyfriend Complexity

Penny asks Leonard to lie to her father, while Howard, Raj and Bernadette pull an all-nighter at a telescope.

4x10 - The Alien Parasite Hypothesis

Amy finds she has sexual feelings for Penny's ex, while Koothrappali and Wolowitz try to prove who would be the better superhero.

4x11 - The Justice League Recombination

The guys find a "super" use for Penny's new boyfriend, Zack, when they enter a costume contest as the Justice League.

4x12 - The Bus Pants Utilization

Leonard's idea for a smartphone app derails his friendship with Sheldon.

4x13 - The Love Car Displacement

Bernadette runs into her ex-boyfriend while attending a science event with Wolowitz.

4x14 - The Thespian Catalyst

Hoping it will make him a better teacher, Sheldon has Penny give him acting lessons. Raj has fantasies about a friend's girlfriend.

4x15 - The Benefactor Factor

A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science.

4x16 - The Cohabitation Formulation

As Wolowitz contemplates taking things with Bernadette to the next level, Leonard rekindles his relationship with Raj's sister.

4x17 - The Toast Derivation

Sheldon becomes concerned when everybody begins to hang out at Raj's apartment and discovers Leonard is the center of the group.

4x18 - The Prestidigitation Approximation

Sheldon is baffled by Wolowitz's magic trick. Meanwhile, Leonard realizes dating Priya may make it impossible to continue being friends with Penny.

4x19 - The Zarnecki Incursion

Sheldon's World of Warcraft online game account is hacked and he is determined to find out who did it. Also Penny shares some girl talk with her friends about Leonard and his new girlfriend. When Howard discovers who hacked the account, the guys depart for a quest to Carlsbad, California where the hacker, Todd Zarnecki, lives in order to retrieve the stolen account, along with "enchanted weapons, gladiator armor, gold, and a battle ostrich, Glenn". Despite Sheldon carrying his Bat'leth with him they fail miserably. On the way back their car engine breaks down, and they're saved by Penny, who came to drive them home and upon hearing about their failure promises to show them "How we finish quests in Nebraska" and forces Zarnecki to give up kicking him below waist.

4x20 - The Herb Garden Germination

Sheldon and Amy decide to start several rumors about the others as a test. Meanwhile, Howard takes his relationship with Bernadette to even higher level.

4x21 - The Agreement Dissection

When Leonard spends too much time in the shower with Priya, Sheldon charges Leonard with two violations of the roommate agreement. However, before he can get too far, Priya uses her skills as a lawyer to nullify the charges due to the agreement's vague wording, much to Sheldon's dismay. When the guys take advantage of Priya's skills in order to eat Greek food on pizza night, Sheldon goes to Penny, who invites him to a girls' night out with Amy and Bernadette, which Sheldon agrees to after Penny mentions that they may be talking trash about Priya. After the girls drink some cocktails, they decide to take Sheldon dancing, which Sheldon reluctantly goes along with. After dancing, Sheldon takes an intoxicated Amy back to her apartment and as well as talking about Priya, meets a monkey who is addicted to smoking cigarettes. Amy tells Sheldon not to give in to Priya's law skills, before kissing him and going to her bathroom to vomit.

4x22 - The Wildebeest Implementation

Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.

4x23 - The Engagement Reaction

When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.

4x24 - The Roommate Transmogrification

When Bernadette receives her PhD, Wolowitz feels emasculated. Raj and Leonard swap places and Penny does something she's regrets.

8x3 - The First Pitch Insufficiency

Howard feels nervous when he is asked to throw the first pitch at a Los Angeles Angels game. Penny and Leonard want to prove Sheldon wrong after he says he and Amy are the better couple.

8x4 - The Hook-Up Reverberation

Raj's honesty comes back to haunt him when his new girlfriend is unfriendly to Penny. The guys think about becoming part owners in Stuart's store.