The Big Bang Theory

Bernadette and Wolowitz leave their kids for the first time; Penny and Leonard try to keep a secret; Sheldon and Amy stick together; and Koothrappali makes a new friend, as the gang travels together into an uncharted future.

Sheldon and Amy await big news.

Leonard is pleasantly surprised when Beverly comes to visit and she's genuinely kind to him, until he finds out the real reason she's there. Also, Denise and Stuart overstay their welcome at the Wolowitz house.

Kripke has proof that Dr. Pemberton plagiarized his thesis in college, and Sheldon and Amy aren't sure if they should turn him in or not. Also, Wolowitz is happily surprised to learn that Bernadette wasn't the only waitress at the Cheesecake Factory who had a crush on him back in the day.

Koothrappali is worried people won't take him seriously in his own field after publishing a paper that suggests he may have discovered alien life. Also, Leonard wants to be the principal investigator on a plasma physics study.

The concept of what it would mean for women everywhere if Amy were to win a Nobel Prize causes Amy to have a meltdown. Also, Koothrappali and Wolowitz try to relive the good old days after Wolowitz buys a scooter that looks like the one he had years ago.

When competitors Pemberton and Campbell charm America on a publicity tour, Sheldon and Amy try to bring Nobel laureates Kip Thorne, George Smoot and Frances Arnold to their side. Also, Halley�s fear of the dark leads to opportunity and conflict for Howard, Bernadette and Stuart.

When Penny and Bernadette go to San Diego for a pharmaceutical sales convention, Wolowitz is in charge of the kids. Also, Sheldon finds a book on experimenting on kids, and the guys plus Amy make a day of it.

The gang finds out Wil Wheaton hosts a celebrity Dungeons and Dragons game involving William Shatner, Joe Manganiello, Kareem Abdul-Jabbar and Kevin Smith. Deception and betrayal are the path to make it to the one open seat.

Penny tries to seduce an abstaining Leonard to ruin his "donation" for her ex-boyfriend, Zack, and his wife, Marissa. Also, Wolowitz, Bernadette, Anu and Koothrappali turn Koothrappali's canceled bachelor party into a couple�s trip aboard the "vomit comet."

Sheldon is thrilled to help Bernadette and Wolowitz navigate bureaucratic paperwork, until he discovers they are breaking the law. Also, Leonard is disappointed when his friends exclude him from a scientific project.

Sheldon and Amy's super asymmetry theory is proven by two physicists, Dr. Pemberton and Dr. Campbell from Chicago, who then try to kick Amy off the Nobel nomination. Also, Bernadette has a big success at work and Penny's going to be a part of it�whether she wants to be or not.

Penny's ex-boyfriend, Zack, and his wife want a baby, but when Zack is infertile, they ask Leonard for help. Also, Koothrappali attempts to mend things with his ex-fianc�e, Anu.

Penny and Leonard organize a paintball game that results in mayhem when Sheldon is jealous of Amy. Also, Koothrappali catches Anu with her ex-boyfriend, and Stuart doesn�t want to move in with Denise.

Sheldon and Amy are still down about their theory being disproven, but a VHS tape from Sheldon�s past inspires him not to give up. Also, Bernadette turns into a pageant mom when she tries to help Wolowitz ace his Magic Castle audition.

Sheldon and Amy are devastated after learning from a Russian paper that Super Asymmetry has already been discovered and disproven. Also, ultra-competitive Bernadette asks Stuart�s girlfriend, Denise, to teach her how to beat Howard in a popular videogame.

Sheldon tries to bond with Amy�s father, but when Wolowitz lures Mr. Fowler away with magic tricks, Sheldon has no choice but to bond with Mrs. Fowler. Also, Koothrappali and Anu try to get physical for the first time.

Leonard is caught between a rock and a hard place when he�s responsible for distributing extra grant money. Also, Bernadette turns the backyard playhouse into a hideaway from her husband and kids.

When Wolowitz dresses up as Sheldon for Halloween, Sheldon seeks retaliation at Leonard and Penny�s Halloween party. Also, Leonard is shocked that Penny doesn�t remember their first kiss.

When Amy doesn�t have time to work on super-asymmetry, Sheldon goes to great lengths to ensure she�s available to work with him even it if means accidentally sabotaging her career in the process. Also, Koothrappali doesn�t want Wolowitz to join him in hosting a show at the planetarium.

When Sheldon won�t tell anyone why he�s never mentioned Tam, his childhood best friend, Leonard takes matters into his own hands. Also, Bernadette and Penny take out Raj�s fianc�e, Anu, for dinner to get the skinny on her.

The Wolowitzes� life gets complicated when Stuart starts bringing his new girlfriend home. Also, Penny and Leonard talk about starting a family while Koothrappali explores an arranged marriage.

Sheldon and Amy drive themselves crazy trying to figure out what �perfect gift� Leonard and Penny gave them for their wedding. Also, Koothrappali decides he wants to settle down and asks his father to arrange a marriage for him.

Sheldon and Amy�s honeymoon runs aground in New York, while Penny and Leonard discover they are uncomfortably similar to Amy�s parents, Mr. and Mrs. Fowler. Also, Koothrappali insults physicist Neil deGrasse Tyson and starts a Twitter war.

When Amy�s parents and Sheldon�s family arrive for the wedding, everybody is focused on making sure all goes according to plan � everyone except the bride and groom.

When Sheldon learns that his mother won�t attend his wedding unless he invites his brother, Georgie, he and Leonard travel to Texas to end a family feud. Also, the Wolowitz kids inadvertently infects Amy, Bernadette, Wolowitz and Koothrappali with pinkeye.

Sheldon goes to Vegas to win money for science. Also, Penny and Bernadette take Amy wedding dress shopping, but her terrible choice entangles them in a web of lies.

Sheldon�s comic book store experiences changes when writer Neil Gaiman puts Stuart�s store on the map. Also, Koothrappali takes credit for Penny�s astronomical discovery, and friendships are threatened.

A brilliant but reclusive scientist, Doctor Wolcott, invites Sheldon to his cabin in the middle of nowhere, and Leonard, Raj and Howard go along for the trip. Also, Penny and Bernadette improvise after Amy doesn�t like the tame bachelorette party they planned for her.

When Leonard learns Sheldon is the president of the tenants association, he decides to run against him. Also, Bernadette encourages Wolowitz and Koothrappali to find the owner of a drone after they find it in the backyard.

Penny gets the opportunity to host Bill Gates at work when his company wants to partner with her pharmaceutical company. Also, Leonard, Koothrappali and Wolowitz do everything in their power to meet him, while Sheldon thinks he is the victim of an April Fools prank.

Leonard jumps through hoops to help secure the perfect wedding venue for Sheldon and Amy. Also, Bernadette and Wolowitz have a hard time deciding who should stay at home with the kids and who should go back to work.

When Bernadette won't go into labor, all her friends try different tactics to get things started. Also, Wolowitz confronts Bernadette after Amy accidentally reveals she's already chosen their son's name.

When Sheldon petitions Wil Wheaton to appear on the new Professor Proton show, Wil offers a role to Amy instead. Also, Penny gets angry when she thinks the female protagonist in Leonard's novel is based on her.

Koothrappali finds himself in the middle of domestic drama when he learns the woman he's dating, Nell, has a very upset husband, Oliver. Also, when Sheldon rents his old room back for a quiet place to work, he drives Leonard crazy by being a model tenant.

When Sheldon kicks Amy out to work solo, she and Leonard bond during a series of science experiments. Also, Bert the geologist replaces Wolowitz in the band Footprints on the Moon, and Sheldon finds Penny a surprising source of scientific inspiration.

To discover who would be most qualified to be best man and maid of honor at their wedding, Sheldon and Amy subject their friends to a series of secret experiments. Also, Penny reveals her true feelings about Amy.

Sheldon and Wolowitz plan birthday celebrations for Amy and Halley, respectively. Also, Leonard receives a Christmas letter from his brother that causes him to spiral out about his own lack of accomplishments.

Sheldon and Amy try to eliminate stress from wedding planning by applying math to the process. Koothrappali �breaks up� with Wolowitz after realizing his best friend is actually hurting his confidence.

Sheldon tries to teach the guys a lesson after they cut him out of a potentially valuable Bitcoin investment. Also, a seven-year-old video reveals a secret about Leonard and Penny's relationship.

Leonard and Wolowitz are furious after they learn Sheldon went to work with the military behind their backs. Also, while Bernadette is on bed rest, she asks Raj to do some digging when she suspects Ruchi is trying to steal her job.

Sheldon and Bert collaborate on a research project, despite Sheldon's embarrassment. Also, Penny and Bernadette coach Koothrappali on how to navigate his relationship with Ruchi.

Sheldon goes head-to-head with Wil Wheaton for the role of the new Professor Proton. Also, Penny steps in to take care of Halley when Bernadette and Wolowitz both wind up on bed rest.

Sheldon and Koothrappali confide in Bernadette when they can't handle Amy and Wolowitz working together. Also, Penny and Leonard learn new tactics for how to deal Sheldon from an unlikely source.

Wolowitz and Sheldon bond when they drive to the desert to shoot off a model rocket. Also, when Leonard's mom, Beverly, finds a new best friend in Penny, it rubs Leonard the wrong way.

As Sheldon stresses about picking a wedding date, Amy tries to convince him he has a more laid-back side. Also, Koothrappali and Stuart compete to win the heart of Bernadette's new coworker, Ruchi.

Leonard angers the university - and the entire physics community - after he gives an embarrassing interview. Also, Amy and Bernadette bond over having to hide their success from Sheldon and Howard.

Amy gives Sheldon an answer to his proposal while Howard and Bernadette struggle with some unexpected news.

The gang is concerned when Sheldon�s former admirer, Dr. Ramona Nowitzki, resurfaces while Amy is away at Princeton.

After celebrating the completion of the top-secret Air Force project, Leonard, Sheldon and Howard get an unwelcome surprise; Amy receives an offer for a summer position at Princeton as a visiting researcher.

Leonard isn�t thrilled when Penny considers taking a new job offered by her ex-boyfriend, Zack.

Howard and Bernadette have a hard time leaving Halley in day care when Bernadette returns to work. Also, Bert introduces the gang to his new girlfriend, Rebecca.

Sheldon pushes himself to the limit when he collaborates on projects with Leonard and Wolowitz as well as Amy on the same day. Also, Bernadette is nearing the end of her maternity leave and must return to work.

Leonard, Penny and Raj adjust to their new living arrangement and Sheldon takes an interest in Amy's work.

Raj searches for a cheaper living arrangement and it creates unexpected conflict among everyone.

The guys' annual trip to Comic Con is in doubt when Raj can't afford to go and an unexpected replacement is considered.

Sheldon and Amy have their first fight since moving in together, and Koothrappali is shocked at the realities of financial independence when he stops receiving support from his father.

Leonard and Wolowitz try to distract Sheldon when he slows the progress of their guidance system. Also, Penny and Amy take Bernadette out for the night, leaving Raj and Stuart to care for baby Halley.

Sheldon beta-tests an MIT invention after hearing it can help him read people's emotions. Also, Leonard can't hide his feelings when Penny announces her brother is coming to town, and Raj invites his ex-girlfriends over to give him dating advice.

When Penny feels that Leonard is taking her for granted, she decides to go on a spa weekend with Amy. Also, Wolowitz and Koothrappali try to fix a squeaky floorboard in the baby's room.

Sheldon and Amy visit Leonard and Penny for the first time since the holidays and share details about their terrible trip to Texas.

Amy's desire to have an intimate night with Sheldon on her birthday is interrupted by Bernadette going into labor.

Sheldon and Leonard must divide up their possessions and remove Penny's things from 4B. Meanwhile, Koothrappali and Stuart fight to be the most helpful during Bernadette's final weeks of pregnancy.

When Bert, a Caltech geologist, wins the MacArthur Genius fellowship, Sheldon is overcome with jealousy. Also, Wolowitz finds an old remote control Stephen Hawking action figure he invented.

After a successful experiment combining their genes, Sheldon will stop at nothing to convince Amy they should procreate. Also, Koothrappali is embarrassed to tell the gang what the new woman he�s dating does for a living.

In order to continue living with Sheldon, Amy lies to him about repairs being made to her apartment and they host an "on location" episode of "Fun With Flags" in Penny�s apartment. Also, Leonard lets Penny decorate Sheldon�s old room after he learns that she has been secretly moving Leonard�s collectibles into storage.

Penny is surprised to learn she has fans of her performance in "Serial Ape-ist" when she attends Van Nuys Comic Con with Leonard. Also, Amy hosts a Sheldon-style brunch at Penny�s apartment, and Wolowitz makes an impulsive purchase when he starts stressing out about the baby on the way.

Leonard and Penny must separate a quarreling Sheldon and Amy when their cohabitation does not go as planned, and Sheldon threatens to break off their relationship when Amy refuses to adhere to the bathroom schedule. Also, Howard and Bernadette find unexpected guests at their house when they decide to stay home from a planned vacation.

When Amy's apartment floods, she proposes a "cohabitation experiment" with Sheldon. Also, Howard and Bernadette are upset when Koothrappali learns the gender of the baby before they do.

Sheldon can't keep up with the late nights Howard and Leonard are putting in and must resort to ingesting energy drinks to stay awake. Elsewhere, Raj spends the day with a pregnant Bernadette, while Penny and Amy attend a faculty party.

The Air Force shows interest in the guidance system the guys are building and Penny lets it slip at work that Bernadette is expecting.

After Leonard's father, Alfred and Sheldon's mother, Mary share an evening together, everyone deals with an awkward morning the following day. Also, Penny's family arrives for the ceremony, including her anxiety-ridden mother, Susan, and her drug dealing brother, Randall.

Leonard and Penny get remarried in front of their friends, Leonard's parents, Beverly and Alfred and Sheldon's mother, Mary, who finds something in common with Alfred. Howard gets an unknown email from the Air Force about his invention.

Sheldon hires Stuart to spend the day with Amy when he�d rather go to a movie screening. Also, Leonard�s mother, Beverly, comes to town and Penny struggles to make a connection with her.

Sheldon and Bernadette spend a night together while the rest of the gang goes to a wine tasting party, but things get uncomfortable for Raj when Zack also attends and takes an interest in Claire.

Everyone must choose sides when a small argument between Leonard and Sheldon erupts into a heated fight during a group get-together.

Secrets are revealed when Amy and Sheldon join Penny and Leonard on a weekend cabin trip. Raj is more excited about Howard's and Bernadette's impending parenthood than they are.

Amy is shocked at a revelation from Sheldon after she buys him a new laptop. Koothrappali sells out Leonard and Wolowitz after they lie to their wives in order to attend an early screening of a movie.

Sheldon works up a contract to split their portion of their guidance system invention royalties, but Bernadette does not like how it's done. Raj must again decide between Emily and Claire when they both contact him.

After more than nine years together, the gang finally celebrates Sheldon�s birthday, surprising him with a special guest.

When the gang finds out about Bernadette's pregnancy, they celebrate by singing karaoke. Also, Bernadette is concerned when Wolowitz freaks out over her pregnancy announcement, and Wolowitz is convinced he must make more money to provide for a baby.

Sheldon and Amy host a live Valentine's Day episode of Fun with Flags, Leonard and Penny grapple with getting older, Howard and Bernadette find a surprise in their hot tub and Raj is torn between Emily and the cute girl he met at the Comic Bookstore.

Sheldon is thrilled when his Meemaw comes to visit, but his excitement quickly fades when she butts heads with Amy. Also, Raj meets a new girl at the comic book store who makes him question his relationship with Emily.

The gang decides to head to Vegas for the week on a party bus. Sheldon learns about the importance of empathy and saying sorry.

Leonard visits a psychiatrist so Penny can make a sales call. Stuart moves out of the Wolowitz house. Sheldon works with Raj looking for extra-solar planets.

As the guys prepare to go to the premiere of the new Star Wars movie, Sheldon plans a special event for Amy's birthday.

Sheldon has a revelation when he realizes why a song was stuck in his head. Also, Amy invites Dave over for dinner despite their previously awkward date, and Wolowitz and Koothrappali become obsessed with a fan of their band, "Footprints on the Moon."

It�s Thanksgiving. Sheldon and Amy go on a lunch date to the aquarium as friends. Meanwhile, Howard, Bernadette, Raj and Emily help out at a soup kitchen and Leonard and Penny make their first Thanksgiving dinner as a married couple.

Amy has a�formal date which Leonard, Penny and Bernadette secretly spy on.�Sheldon has Howard and Raj help him find a new girlfriend since they found Amy for him.

Adam Nimoy, friend of Wil Wheaton and son of Leonard Nimoy, interviews Sheldon for a "Star Trek" documentary, but Sheldon goes off topic and has trouble suppressing his emotions about his recent break-up from Amy. Bernadette wants to start renovating the house and the issue of starting a family with Howard is brought up.

In the midst of a nation-wide helium shortage, Sheldon and Leonard take desperate measures to get the supplies they need. Also, Penny and Bernadette download a dating app on Amy's phone to try and find her a new man.

The guys take a fencing lesson from Barry Kripke and Sheldon finds himself in an awkward position when Kripke expresses interest in Amy. Also, when Stuart struggles to get female customers at the Comic Book Store, Penny, Amy and Bernadette come by to help him out.

Leonard and Penny finally move in together leaving Sheldon very upset with this big change in his life and wishing he could go back to a time when he had no emotions in 2003 before he met Leonard. Raj, Howard and Stuart attempt to form a band.

The guys� science skills are put to the test when they get a flat tire during Leonard�s bachelor party weekend in Mexico. Also, the girls force Penny to finally tell her family that she eloped with Leonard.

Leonard confronts the woman he kissed on the North Sea in an attempt to set Penny�s mind at ease. Also, Sheldon films a special episode of �Fun with Flags� after his breakup with Amy, and Bernadette feels guilty about withholding a secret from Penny.

Sheldon is confronted by a mystery of the universe he cannot unravel: when Amy presses pause on their relationship. Meanwhile, in Las Vegas, Penny struggles with Leonard's confession that he kissed another girl.

Sheldon pushes Leonard and Penny to choose a date for their wedding and deals with dramatic changes in his own relationship with Amy.

Personalities collide when Sheldon and Leonard�s mothers finally meet. Meanwhile, Howard finally decides to �man up� and do his fair share of the housework � but not without a little help from his friends.

Wolowitz questions his engineering abilities when he and Sheldon can�t get a toy drone to fly. Meanwhile, a cancelled flight nearly prevents Leonard from giving the commencement address at his former high school, and Raj pits his parents against each other when his father cuts him off financially.

When Raj is asked to create a message in case a NASA mission discovers alien life, the guys fight over what he should do. Also, Penny is torn between auditioning for a movie or keeping her successful pharmaceutical sales job.

When Sheldon and Amy build a blanket fort, they come to major crossroads in their relationship. Also, Wolowitz meets the half-brother he never knew he had, and when Penny is invited to appear on Wil Wheaton�s podcast, she and Leonard have a huge, on-air argument.

When Leonard and Sheldon are invited to speak at UC Berkeley, they take a detour to try to meet an idol. Also, when Bernadette and Howard battle over the fate of his Doctor Who TARDIS, Raj and Amy offer to settle the dispute with a game of ping pong.

Friction ensues when a magazine fails to mention Leonard in an article about the paper he co-wrote with Sheldon. Also, a blackout at Mrs. Wolowitz�s home leads to a final family dinner in her honor.

Trouble arises when Amy learns Sheldon has applied for a one-way mission to colonize Mars. Also, a trip to the pet store ends in a fight for Sheldon and Amy, Leonard surprises Penny with a very �adult� purchase, and Raj is caught snooping in Emily�s apartment.

As a joke, Sheldon and Penny try an experiment designed to make participants fall in love. Also, Leonard, Amy, Raj and Emily spend the evening trying to escape a room with a �zombie.� And, after returning from Mrs. Wolowitz� funeral, Bernadette and Howard run into trouble at the airport.

Wolowitz receives some shocking news as everyone prepares for the reopening of Stuart�s comic book store. Penny teaches Sheldon how to �let it go,� but can�t follow her own advice after she learns something infuriating about Amy. Also, Leonard and Raj think they've spotted Nathan Fillion at a restaurant.

Leonard and Sheldon publish a paper which is widely accepted except for comments from an internet troll. Meanwhile, the girls reminisce about embarassing incidents from their past.

The gang tries to help Sheldon when he becomes stuck in a rut at work by increasing his anxiety level. Howard teases Raj with a new game called "Cinnamon or Emily?"

Wolowitz tries to distract Raj, who is anxiously awaiting data from a space probe he helped launch. Meanwhile, Sheldon and Leonard go dress shopping with Penny and Amy.

Leonard and Howard turn to Raj for help in dealing with a work emergency when they nearly come to blows after blaming each other for a potential disaster at the university. Amy throws an authentic Victorian Christmas party, while Sheldon seeks revenge on her for making him celebrate the holidays.

While Sheldon says a tearful goodbye to the final installment of "Fun with Flags," Leonard, Howard and Raj search for something significant in a dead professor's research and Bernadette is shocked to learn of her co-workers� true feelings from Penny.

When Leonard gets minor surgery on his nose, Sheldon is the one in need of sympathy. Meanwhile, Raj's parents' impending divorce causes Howard and Bernadette to work on their own marriage.

When the gang recreates a high school prom night on the roof of the guys' apartment building, Sheldon feels pressure to participate in all the typical romantic traditions.

The guys try to help Penny out of an awkward work dilemma, when a smitten doctor shows up at her door after her flirtatious sales techniques work a little too well. Meanwhile, Amy and Bernadette argue over whether or not female scientists should play up their sexuality.

Sheldon and Raj test whether they could survive a dark-matter research expedition in a salt mine by simulating the conditions in a steam tunnel deep underground. Leonard and Penny seek advice from Howard and Bernadette after they fight about money.

During their weekend in Las Vegas, Bernadette and Amy accuse Penny of being a buzz kill; the guys try to invent the next big thing, but only succeed in procrastination.

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.

Wolowitz feels nervous when he is asked by NASA 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.

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

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

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.

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.

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.

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.

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

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

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.

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.

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.

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.

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.

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.

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.

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

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.

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 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."

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 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.

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.

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.

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.

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.

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.

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

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

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.

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

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

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

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

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.

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

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.

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.

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

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

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

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

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

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

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

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

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

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

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

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

As Howard's mission to space approaches, Howard and Bernadette decide to get married before his launch, causing the gang to scurry into overdrive in an effort to stage the wedding.

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.

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

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

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.

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

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.

Sheldon and his rival Barry Kripke fight it out over the availability of a new office. Penny gets a gift from Amy that really tests their friendship and it doesn't end well.

When Sheldon is forced to take his vacation, he goes to work with Amy in her neurobiology lab. Also, Bernadette wants Howard to sign a pre-nup.

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

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. Meanwhile, Sheldon decides to start a YouTube series entitled "Sheldon Cooper presents Fun with Flags" with the help of Amy.

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

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.

When Leonard's former high school tormentor resurfaces, Leonard must confront him. Meanwhile, Penny realizes she did her fair share of tormenting in the past.

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

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.

Amy becomes heartbroken when she discovers that Penny and Bernadette went wedding dress shopping without her and turns to a reluctant Sheldon for comfort.

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

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.

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

Penny plays Matchmaker for Raj, which results in him finding a girl he is comfortable talking to, but the gang suspects that she may be taking advantage of Raj.

Leonard and Amy get to know each other better when Amy invites Leonard to a wedding. Meanwhile, Howard and Bernadette spend the weekend with Mrs. Wolowitz.

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

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.

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

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

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

When Priya finds a loophole in the roommate agreement to throw Sheldon out for the night, Penny, Amy and Bernadette take him to a nightclub.

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

The guys go all out to help Sheldon find the person responsible for hacking his online gaming account, while the girls' hatred for Priya increases.

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

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

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

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

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

When the gang road trips to a conference, tensions run high when Bernadette runs into her ex-boyfriend.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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.

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.

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.

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

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

When Penny has an old friend staying over at her apartment, an argument ensues between her and Leonard, causing Sheldon to get caught between the couple.

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

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.

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.

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

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.

When Sheldon learns the guys tampered with his expedition data he got from the arctic, he returns 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.

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

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.

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

When a fellow comic book enthusiast hits on Penny it leads to Leonard and Howard going to a bar's on Ladies' Night.

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

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

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

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

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

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

Sheldon creates a scientific procedure for making friends.

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.

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

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

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

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

When Sheldon bans Penny from the apartment for numerous minor infractions, she decides to retaliate. Meanwhile, Howard and Rajesh try to find the house where all the models from "America's Top Model" are staying.

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

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

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

Sheldon creates a monster when he introduces Penny to online gaming. Meanwhile, Sheldon disagrees with Leslie Winkle at work.

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

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

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

Penny wants to throw a surprise party for Leonard, but Sheldon's indulgence at an electronics store throws her off-track. Meanwhile, Howard makes a terrible sacrifice for the sake of the surprise.

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.

When the guys buy a time machine prop from a classic 1960 movie, Penny lashes out at Leonard and he decides it's time to give up his habit, much to his friends' protestation.

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

When Sheldon meets a 15-year-old physicist prodigy, he's rattled and threatened and Leonard tries to help him look for ways to debunk his research.

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.

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

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.

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

When Wolowitz seduces one of Penny's friend who then takes over her apartment, Penny sleeps on Leonard and Sheldon's couch. Meanwhile, Penny is recruited to fill in for Howard on the guys' Halo team.

Penny hosts a Halloween party, that ends up putting Leonard, Sheldon, Wolowitz, and Koothrappali through a new test of their social skills.

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

When Sheldon gets fired and decides to explore life beyond physics, it's up to Leonard to take drastic action to snap his friend out of his funk.

When Leonard learns Penny is seeing someone, he decided to asks a nerdy female co-worker out on a date.

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.

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.