The very first pilot of The Big Bang Theory. Leonard and Sheldon make spending money by donating to a sperm bank and later meet an attractive young woman in distress, who they decide to help.
Young scientists Sheldon Cooper and Leonard Hofstadter work at Cal Tech and lead quiet and uneventful (though nerdy) lives. Then a beautiful blonde aspiring actress named Penny moves into the apartment across the hall. She quickly changes things.
Songs: Mac Davis
-- Baby Don't Get Hooked On Me
After bringing a package of furniture into Penny's apartment, Sheldon is appalled at the uncleanliness of the place so he sneaks inside one night to clean it. Needless to say, Penny is not thrilled.
After Leonard sees Penny with a new guy he tries to trick her into going on a date with him.
An argument with the new head of the Physics Department leaves Sheldon without a job. He then proceeds to drive the guys and Penny crazy with his antics so Leonard calls his mother in order to set his friend back on course.
Cello playing Leonard joins a music ensemble at the university which leads to a sexual encounter with fellow ensemble member Leslie Winkle. Sheldon, who despises Leslie, disapproves of this relationship.
Songs: Bryan Adams
-- Have You Ever Really Loved A Woman?
Penny invites the guys to a Halloween costume party at her apartment. Once there, Leonard gets into an argument with Penny's hulking ex-boyfriend.
Penny's slutty friend from Omaha, Christy, pays her a surprise visit and it doesn't take long for her to hook up with Howard Wolowitz. When Howard starts hanging out with Kristy it takes the others, especially Sheldon, time to adjust to his absence.
Raj discovers that he can talk to members of the opposite sex after he's had a few drinks so he reluctantly heads out on a date arranged by his parents with a girl whom he knew in childhood.
Leonard and Sheldon's research paper is accepted for publication and Leonard wants to present it at a conference. Unfortunately, Sheldon wants no part of the presentation.
In order to cover up a lie he and Leonard told to Penny, Sheldon concocts an even more elaborate lie involving a fictitious drug addicted cousin.
Songs: (Unknown artist) -- Out Tonight
When Sheldon gets sick the guys bail out and head for a Planet of the Apes marathon at a nearby movie theater. This leaves Penny the task of caring for the ailing eccentric genius.
Songs: THX -- Deep Note, (Unknown artist) -- Soft Kitty
Sheldon becomes jealous of a newly hired 15 year old Korean scientific prodigy.
Songs: (Unknown artist) -- Cielito Lindo
The guys form a team for the upcoming Physics Bowl tournament at the university but when Sheldon annoys everyone else on the team to death he gets kicked off and replaced by Leslie Winkle. Determined to win the contest, Sheldon forms his own team.
-- We Are The Champions
They guys buy a prop from the movie The Time Machine off Ebay but when transporting the machine up to the apartment causes Penny to miss work she let's them have it in no uncertain terms.
When Sheldon's attractive twin sister, Missy, pays her brother a visit, Leonard, Howard, and Raj all try to make time with her to Sheldon's disapproval.
Penny decides to throw Leonard a surprise birthday party after learning he never had one as a child but things go awry quickly after she asks Sheldon for help with the party.
After Penny breaks up with her latest boyfriend Leonard finally musters up enough courage to ask her out on a date. She says yes and then goes to Sheldon for advice.
Leonard and Penny's date ends abruptly then she goes to Sheldon for advice and reveals a secret about herself which he has a hard time keeping.
After Leonard sees Penny with a new guy, he hooks up with Leslie Winkle again but the relationship hits a snag when he supports one of Sheldon't scientific theories over hers.
Introduced by Sheldon to a video game, Penny soon becomes addicted to playing it to the detriment of everything else in her life.
Raj gets all full of himself after making a scientific discovery and receiving a subsequent award from People magazine.
The gang stages an intervention with Sheldon in order to force him to learn how to drive after their playing chauffeur for him begins imposing upon their time and driving them crazy.
A graduate student takes a liking to Sheldon and soon begins doing all his daily tasks. Our hero likes it at first but her devotion soon proves to be too much.
War breaks out between Penny and Sheldon when he banishes her from the apartment for touching his food. Meanwhile, Raj and Howard try to find the location of a house full of super models.
Howard goes on a date with a woman but when she meets Leonard she quickly ditches Howard. This leads to tension between the two nerdy friends.
Sheldon wholeheartedly approves of Leonard's new relationship with Stephanie and takes steps to see that it continues.
Guest Stars: Sara Rue
as Dr. Stephanie Barnett
When Leonard decides that he wants to end his relationship with Stephanie he goes to Penny for advice on how to do so.
Guest Stars: Sara Rue
as Dr. Stephanie Barnett
A handsome colleague of Leonard's asks Penny out on a date. Meanwhile, Sheldon struggles to come up with an appropriate Christmas gift for Penny.
The guys build a killer robot and are challenged to a duel by a colleague at the university. Meanwhile, Penny lays down the law towards Howard regarding his behavior towards her which causes him to go into a deep depression.
Songs: Howard Wolowitz -- My Girl (Marcie Grossman)
When Sheldon discovers that nemesis Kripke is in charge of access to the university's super computer he decides to befriend his badly lisping colleague in hopes of gaining access.
Sheldon lends Penny money when she is unable to pay her rent. Leonard then tries to discover why she is in such a financial bind and finds out it has to do with her hulking ex-boyfriend Kurt.
Leonard's mother arrrives for a visit and proceeds to drive him, Penny, Howard, and Raj crazy. Sheldon, however, finds her fascinating and the two get along extremely well.
Penny panics when she accidentally shoots a paintball pellet onto the cushion in Sheldon's spot on the living room couch. Meanwhile, Howard begins a sexual relationship with Leslie Winkle.
The guys travel on board a train to San Francisco for a symposium and discover that actress Summer Glau is also on board. Howard, Raj, and Leonard then develop plans to make time with her. Sheldon must rely on Penny's help after discovering that he left his flash drive behind.
Penny starts he own internet business but a caffeine addled Sheldon doesn't exactly help her make it into a success.
Penny get extremely jealous when a beautiful new girl moves into the apartment building and immediately has the guys at her beck and call doing favors.
Stuart, the owner of the comic book store, gets Penny to go out on a date with him but it ends up getting ruined by Sheldon's interference. Meanwhile, Leonard, Howard, and Raj head for a single's bar to pick up women and one of them gets lucky.
After Leslie Winkle breaks up with him, Raj and Leonard take Howard to Las Vegas in order to cheer him up. A prostitute they meet there named Mikayla might be just what Howard needs. Meanwhile, Sheldon, who has stayed behind, finds himself locked out of the apartment.
Songs: Kaley Cuoco -- Soft Kitty
A second date between Penny and Stuart ends disastrously when she calls out Leonard's name during a make-out session. Meanwhile, Howard tries to fix a design flaw in a NASA space station toilet with some help from his friends.
When Sheldon is chosen by the university to lead a scientific expedition to the North Pole he persuades his reluctant friends to accompany him as members of his research team. When hearing the news, Penny is sad because she realizes that she will miss Leonard while he's gone.
The guys return from the North Pole but when Sheldon finds out that they tampered with the results of his experiment there he leaves for Texas in disgrace. Going to Texas to bring him back prevents Leonard from hooking up with Penny.
Songs: Kaley Cuoco -- Soft Kitty
Leonard and Penny's first night together is awkward. Howard and Sheldon have a major dispute over the species of a cricket found in the apartment.
Sheldon discovers a way to get Penny to "behave" better while Howard and Raj dress as Goths and head to a Gothic nightclub in order to pickup women.
Raj's work visa is up and his research has come to a screeching halt. The only way he can avoid returning to India is to take a job working for Sheldon.
Howard gets Leonard and Penny to set him up with one of her co-workers at the Cheesecake Factory and the double date goes surprisingly well. Meanwhile, Sheldon has a showdown at a card game tournament with nemesis Wil Wheaton.
Seeking to learn more about football in order to impress some of Penny's friends Leonard seeks assistance from an unlikely source--Sheldon.
The relationship between Leonard and Penny hits its first bump when they have an argument about an old musician friend of hers from Omaha who's arriving in town and wants to sleep on her couch. Sheldon, who hates controversy and arguments, tries to play the peacemaker.
When Leonard, Raj, and Sheldon head out to the desert to watch a meteor shower, Sheldon is looking forward to a night alone but must come to Penny's aid when she falls in the shower and dislocates her shoulder. Meanwhile, out in the desert, hilarity ensues when they guys consume some drug laced brownies.
Songs: Kaley Cuoco, Jim Parsons -- Soft Kitty
When Kripke pranks Sheldon during his appearance on National Public Radio our hero is determined to seek an exquisite revenge. Meanwhile, Howard begins to have second thoughts about his relationship with Bernadette.
Songs: Simon Helberg -- Bernadette
Trying to learn more about Leonard's job, Penny approaches Sheldon to teach her more about physics. Howard becomes jealous with Bernadette and Leonard start getting along.
Leonard's mother pays him another visit to his and Penny's consternation and Sheldon's delight.
Leonard and Penny have an argument when he discovers that she believes in psychics while Sheldon and Raj meet two girls at a university mixer and invite them back to the apartment.
Leonard and Sheldon return home one night to discover that their apartment has been robbed and ransacked. This causes Sheldon to come unglued and make a decision to move to Bozeman, Montana.
After getting stumped by a difficult physics problem, Sheldon cracks up and eventually goes to work with Penny at the Cheesecake Factory in order to find a solution.
Songs: Murray Head -- One Night in Bangkok
After being invited to Switzerland to see the CERN Supercollider, Leonard wants Penny to join him and make it a romantic Valentine's Day getaway. Sheldon then tries to do anything to take Penny's place. But what will Leonard do when both get sick?
Ruining his one and only chance at meeting Stan Lee, Sheldon winds up in traffic court because of illegal driving that he did when he drove Penny to the hospital (episode 308). However, as Leonard, Howard and Raj are all going to see Stan Lee, Penny is Sheldon's only hope of avoiding jail.
Special Guest Stars: Stan Lee
as Himself |
The guys buy a box of junk at a garage sale and find something precious inside, a prop ring from The Lord of the Rings that causes friend to go against friend.
Sheldon wins an award and is reluctant to accept it since he must give a speech before a large crowd. Each of his friends tries to help in his/her own way.
Songs: Jim Parsons -- The Element Song
Leonard's relationship with Penny hits rocky water after he utters the "L" word. The guys take on a team led by Wil Wheaton in a bowling tournament.
With Leonard and Penny now split-up, Sheldon becomes the peacemaker.
Sheldon has a famous female physicist friend stay with he and Leonard and becomes upset when Leonard and his friend become intimate.
Leonard and Sheldon's argument leads to Leonard sleeping on Penny's couch and relating how he met Sheldon. The story of the broken elevator also is revealed.
Penny realizes that after dating Leonard, she can no longer put up with the guys of limited intelligence that guys she normally dates. Howard and Raj try to find Sheldon a date on the Internet.
Howard borrows a robotic arm from work and finds himself in a bind, literally. Penny accompanies Sheldon on his first date with new galpal Amy.
Sheldon obsesses over his limited lifespan and takes steps to ensure he will stay alive until it is possible to have his consciousness downloaded into a robot.
After breaking up with Amy, Sheldon turns to feline companionship much to the dismay of all. Leonard calls on Sheldon's mother to set his roommate straight once again.
Howard receives dating advice from Katee Sackhoff and George Takei while Sheldon and Raj engage in a nasty battle over office furniture.
All of the guys have girlfriends except Leonard who asks Howard to set him up with one of Bernadette's friends. Sheldon decides he would be better off without Amy.
When Raj's sister comes to town, Leonard rekindles a romance with her and seeks to keep that information secret from Raj with the voluntary help from Sheldon.
Howard's new project requires he get a security clearance and Sheldon's interview during the background check causes trouble. This leads to Howard terminating their friendship and Sheldon searching for a way to patch things up.
The guys decide to wait in line for a special screening of Raiders Of The Last Ark while the girls pass and have a slumber party.
Penny's father shows up and she asks Leonard for help by pretending to still be her boyfriend. Bernadette joins Howard and Raj spend the night using a telescope as part of an astronomy project.
A chance encounter with Zack, one of Penny's ex-boyfriends triggers an emotional response in Amy. Howard and Raj compete to decide who is a better superhero.
After insulting Zack, Penny's new/old boyfriend, the guys make friends and ask him to help with their entry into a New Year's Eve costume contest.
Leonard has an idea for a smartphone app but as usual Sheldon tries to take over. After being kicked off the team, Penny tries to play peacemaker for him with the others.
The group goes on a road trip to attend a science event and Howard is dismayed when Bernadette encounters an ex.
Sheldon turns to Penny for acting lessons as a way to improve as a teacher. Raj has inappropriate fantasies about Bernadette.
The guys attend a formal dinner to try to persuade wealthy patrons to donate to the physics department. Leonard has to decide how far he will go when a particular donor shows an interest in him.
Howard and Bernadette consider moving in together; Leonard resumes dating Raj's sister, over Raj's vehement objections.
Sheldon decides to invite new friends over when Leonard and the rest of the gang move their gatherings to Raj's place.
Songs: John Ross Bowie, Brian Thomas Smith -- Don't Go Breakin' My Heart, Kevin Sussman, John Ross Bowie, Brian Thomas Smith -- Walking on Sunshine
Priya asks Leonard to choose between her and his friendship with Penny. Howard shows Sheldon a magic trick that Sheldon is determined to figure out.
After Sheldon's World of Warcraft account is hacked, the guys take it upon themselves to confront the culprit.
Sheldon and Amy spread gossip about various members of the group as a social experiment. Howard must decide whether to pop the question to Bernadette.
Priya's increased presence at Leonard and Sheldon's apartment causes changes that Sheldon struggles with. To relax, he accompanies Penny and the girls on a night out with dancing.
Co-Guest Stars: Tom Yi
Amy convinces Penny and Bernadette to use Bernadette as an undercover informant on Leonard and Priya's relationship. Raj decides to try out a new drug to cure his social anxiety disorder, but the results are less than satisfactory.
Howard musters up the courage to tell his mother that he is going to marry Bernadette. The news doesn't sit well and she ends up in the hospital.
Co-Guest Stars: Sharon Omi
as Nurse in Biohazard Suit
Bernadette becomes the latest person in the group to receive her Ph.D., which leads to Howard being teased about his lack of the same. When Leonard starts spending the night with Raj's sister, Raj resorts to becoming a temporary roommate of Sheldon's.
Songs: Vanilla Ice -- Ice Ice Baby
Penny must deal with the aftermath of her night with Raj and how it affects her friendship with the guys. Sheldon names himself captain of the paintball team and tries to assert his leadership.
Sheldon insists Penny rid her apartment of a piece of "found" furniture and tries to use Amy as a go between. Leonard and Priya try to make their long distance relationship with spicy video chats.
Leonard accompanies Amy as her date to a wedding and ends up having fun in spite of himself. Bernadette tries spending the weekend with Howard and his mother in their house.
Raj is depressed and alone Penny fixes him up with a deaf girl to whom he can speak. Unfortunately for our hero, she turns out to be a user.
Sheldon's arch nemesis Wil Wheaton invites the guys to a party at his house and Leonard decides to go, angering Sheldon. Howard gets the opportunity of a lifetime but his decision doesn't sit well with Bernadette.
Sheldon's mom comes to town for a visit and Sheldon is angry that she doesn't want to cook and spend all her time with him. Instead, she chooses to spend most of her time with Leonard and the rest of the gang as they show her the town.
Songs: Laurie Meltcalfe -- Soft Kitty
Leonard is tempted to stray on Priya when a cute girl comes on to him at the comic book store. The guys pull a Halloween prank on Sheldon and he vows revenge.
Sheldon must suffer the responsibility to comfort Amy when Penny and Bernadette exclude her from their pre-wedding shopping.
Songs: Mayim Bialik -- Everybody Hurts
Leonard and Penny decide to spend a night out just being friends. Sheldon freaks out when a bird haunts the apartment.
Sheldon must step up his game with Amy when she decides to go out with Stuart from the comic book store.
To Leonard's surprise, a bully from his high school days and his own personal tormentor gets in touch with him and Leonard must decide on a course of action. The girls try to help Penny make amends for her own history of being a bully.
Amy is upset with Sheldon and his dismissal of her career accomplishments. Howard is dismayed by Bernadette's apparent disinterest in kids.
Out of the blue, Leonard invites Penny out on a date and they struggle with what it means.
Leonard proposes that he and Penny treat their dating like software development and report "bugs" to each other. Raj gets a new phone, and falls in love with the AI contained within.
Leonard finally tires of Sheldon's thankless demands on him and breaks the friendship agreement. Howard and Raj brainstorm a way to make the other NASA astronauts pick a cool nickname for Howard.
Sheldon's is required to take some vacation time away from work, and Amy pays the price. A pre-nuptial agreement rears its ugly head between Howard and Bernadette.
Sheldon and his nemesis Kripke both want an office that becomes available with the retirement of a senior physicist. Amy gives Penny a heartfelt gift that Penny abhors, but how does she tell Amy without hurting her?
When Sheldon's barber becomes unavailable due to illness, it starts the descent of his orderly life into chaos. Astronaut training proves more difficult for Howard than expected.
The guys decide to spend the weekend playing video games like they used to. The women in their life have other ideas however, especially Amy who is counting on Sheldon accompanying her to a family event.
Raj finally gives up and asks his parents for help to find a wife. Sheldon's conscience causes him to hear his toy Spock doll speak to him.
Howard takes advantage of Sheldon's obsession to meet visiting professor Stephen Hawking by putting him through the ringer.
Howard's bachelor party results in Bernadette learning things about Howard's past that makes her reconsider marrying him.
Howard's mission into space gets rescheduled sooner, creating a conflict with the wedding. Leonard and Penny resume their physical relationship until Leonard says something he shouldn't in the boudoir. Amy uses psychology on Sheldon to bring them closer together.
Bernadette decides she wants to be married to Howard before his mission to space. The gang scrambles to get it done.
With everyone paired up, Raj is left alone and imposes himself on others. Howard cannot escape the two women in his life, even while on the space station.
Penny confides to Amy and Bernadette that she is unsure about staying with Leonard, and when Sheldon inevitably learns about it, he takes matters into his own hands. Howard gets pranked as the new guy in space.
Sheldon hires a young woman to be his assistant, which initially makes Amy jealous, then later Penny finds cause for concern. On the space station, Howard starts to freak out when he learns his return to Earth will be delayed.
Howard is home, but on his first night back Bernadette gets sick so he decides to visit his friends. His reception is not what he expected. Game Night with Sheldon, Leonard, Penny and Amy takes a competitive turn when the girls take on the guys.
Raj and Stuart throw a Halloween bash at the comic book store. Howard is upset when everyone tires of his stories about life on the space station. Leonard shows Penny his laboratory and is surprised by her reaction.
Penny reveals that she is taking a class at the local community college, but insists it is no big deal. Sheldon plays an Internet game with his idol, Stephen Hawking, then frets when Hawking stops playing.
Bernadette puts her foot down about Howard moving out of his mom's house. Sheldon is perplexed with the enmity between Amy and his friend Wil Wheaton and has no clue how to fix it.
Howard is curious why Sheldon disappears every day at 2:45 and asks Raj to help him discover the secret. Penny's new school partner causes Leonard to be jealous.
The University decides to reassign Sheldon's unused parking space to the newly popular Howard, a move that Sheldon feels is a slap in the face to his importance. This starts a feud between the two friends that spills over to their ladies, and Penny pays the price.
When Amy gets sick, Sheldon is required to take care of her and she milks it for all it's worth. Bernadette arranges for Howard and her father to bond via a fishing trip.
Leonard leads the boys on a Christmasy version of Dungeons and Dragons, while Raj joins the girls on their night out and they try to find him a girl.
Sheldon manages to put his foot in his mouth and ends up being accused of sexual harassment. In typical fashion, he throws his friends under the bus too.
The guys head out to a comic book convention and get stranded in full costume when Leonard's car is stolen. The girls decide to try to understand their men and end up in a heated debate over a comic book character.
After being forced to team up with Barry Kripke by management, Sheldon is dismayed when he discovers his work is not up to par with Kripke's. Howard and Raj spare no expense to get action figures that look like themselves.
Leonard finally has enough of Sheldon and moves out, to Penny's distress. Amy takes advantage of Sheldon's need for a new roommate, to Sheldon's distress. While Howard is away, Raj agrees to look in on Mrs. Wolowitz, to his distress!
The three couples celebrate Valentine's day in their own way, with little success while Raj and Stuart throw a party for their unattached friends.
When Raj gets dumped again, he decides to never leave his apartment or have anything to do with girls. Penny uses her acting skills to help Sheldon with his "Fun With Flags" videos.
While Leonard, Sheldon, and Howard try to motivate middle school girls to pursue a career in science, the ladies play hooky and go to Disneyland. Raj has a first date with Lucy.
Howard and Bernadette trick Sheldon into organizing their closet where he finds an unopened letter from Howard's father. Howard then struggles whether or not to read it.
A tenured position becomes available at the University and Leonard, Sheldon, Raj, and the lisping Barry Kripke all decide to apply, each with their own unique style of currying favor.
Raj's curiosity about his new love interest leads him to discover something to make him change the impression he makes on people. Meanwhile Penny worries that she lacks passion about anything and Amy tries to cure Sheldon of his completion compulsion.
Sheldon learns that his childhood television idol, Professor Proton, is still alive and hiring himself out for parties, so of course Sheldon hires him to perform. Raj is away for the weekend so he asks Howard and Bernadette to look after his dog, with the expected result.
Special Guest Stars: Bob Newhart
as Arthur Jeffries (Professor Proton) |
Songs: Jim Parsons -- Soft Kitty
The girls join the boys in a game of Dungeons & Dragons after their trip to Las Vegas falls through. Raj and Lucy continue their dating adventures and Raj pushes Lucy to confront one of her greatest fears.
Leonard gets an opportunity to work with Dr. Stephen Hawking, but the downside is it will mean being away for up to four months. Both Penny and Sheldon are affected tremendously and both try to come to terms with their feelings while still supporting Leonard. Raj risks everything with Lucy when he pushes her too hard and too fast.
Sheldon and Penny commiserate over their mutual sadness of Leonard's absence. Howard encourages Raj to start looking for another girlfriend and is surprised at who he chooses. Amy & Bernadette are away at a conference and bond/clash when they talk about their relationships.
Leonard arrives home early and chooses not to tell Sheldon. Howard's unusual behavior results from an unlikely source.
After the entire gang passes on Raj's dinner party, he designs a scavenger hunt that brings out unknown personality traits in his friends.
Sheldon looks to exact revenge from Amy after she ruins Raiders of The Lost Ark by revealing a plot hole. Leonard uses guilt as leverage over Penny, and Raj and Stuart try the Internet to find a date.
When Amy starts working at the same university as Sheldon, friction between the pair spreads to Howard and Bernadette.
Sheldon is insufferable after making a major scientific discovery, or did he? Howard plans an elaborate romantic celebration for Bernadette and Penny decides she needs to do something for Leonard.
Songs: The Big Bang Theory Choir -- Bernadette
A chance encounter with Professor Proton ends up hurting Sheldon's feelings when his childhood hero looks to Leonard for professional advice. Raj's special bonding time with the girls is hijacked by Howard.
Special Guest Stars: Bob Newhart
as Arthur Jeffries (Professor Proton) |
Leonard uncovers a situation that he is sure will make Sheldon "freak-out", but Sheldon comes up with a compromise that ends up punishing Leonard. Penny encounters Raj's ex-girlfriend and can't help herself from intruding into his love life.
Howard invites everyone to his mother's house for Thanksgiving where unexpected drama emerges from Penny's past and Howard's father-in-law bonds with an unlikely person.
Sheldon's disgust at his accidental discovery and subsequent fame reach a level that compels Leonard and Amy to try to mollify him. Raj needs a temporary place to stay for a week so Howard invites him to stay with he and Bernadette.
Sheldon goes home to Texas to be with his family during the birth of his sister's baby and the gang reminisces about what their life would be life if they never met him.
Penny finally gets her big break, or does she? Her reaction leads her to make Leonard an offer that is difficult for him to accept. Sheldon tries to quantize humor while Raj and Stuart go to the mall to practice talking to girls.
Penny takes a drastic step to further her career. While Leonard says he supports her decision, he has his doubts. Sheldon is forced to take some vacation time and ends up hanging with Penny. While Amy fends off an unwanted suitor, Bernadette tries to find a replacement comic book she accidentally damaged.
The guys fail to get tickets to Comic-Con and debate whether to buy them from a scalper. Sheldon refuses to and decides to start his own comic book convention and he targets James Earl Jones as a potential panelist. While the guys are occupied with "childish" endeavors, the ladies decide to do something "grown-up".
Amy treats Sheldon to a train trip as incentive for a romantic Valentine's Day getaway. Raj leaves his dog in the not so capable hands of Penny and Leonard.
At Penny's urging, Leonard stands up to Sheldon and buys a dining room table while Howard and Bernadette contemplate a return to the space station for Howard.
Howard takes Bernadette's comments seriously about he and Sheldon's bickering and invites Sheldon to fly with him to NASA at Houston. Penny's career luck continues its downward slide while Raj asks Amy to be his wingman on an online dating service.
Sheldon decides to surprise his mother with a visit since he is already in Texas with Howard, but he is the one who gets the big surprise. Raj puts on another of his dinner parties that leads to some conflict within the group.
An episode about choices: Raj is faced with the possibility of dating two women; Penny must decide whether to take a role in a bad movie; Sheldon must choose between buying an X-Box One or PS4.
Sheldon comes to the depressing realization that is life long research into string theory has been for naught. Howard and Bernadette join Raj and his new girlfriend Emily on a double date, which turns out to be a night Howard would just as soon forget.
Penny encourages a return to "Anything Can Happen Thursdays" as a way of getting Sheldon's mind off his career funk. Amy and Bernadette get caught in a lie while Howard helps Raj prepare for his date night with Emily.
The loss of Sheldon's idol Professor Proton provokes feelings that Sheldon cannot seem to process. Leonard enjoys torturing Penny about their numerous marriage proposals while Amy and Bernadette decide to make a surprise to help celebrate "Star Wars Day."
Special Guest Stars: Bob Newhart
as Arthur Jeffries (Professor Proton)
Penny's role in the gorilla movie leads her to rethink the choices she has made, both in her career and her life. Howard and Bernadette care for an injured Mrs. Wolowitz, a dry run for a potential child down the road while Raj seeks advice from Sheldon when he sees Emily on a date with another man.
The realization of Leonard and Penny's engagement and future without him suddenly sinks in to Sheldon, and the stress it adds to his already failing career induces panic. Meanwhile, Howard and Bernadette desperately search for assistance caring for Howard's mother.
Leonard and Amy end up taking an unexpected road trip to Arizona to go get Sheldon. Penny has an interview for a job at Bernadette's company. Stuart's relationship with Mrs. Wolowitz freaks out Howard.
After Sheldon is forced to teach a class, Howard manages to surprise everybody by taking it. Amy plays both Penny and Bernadette as the tension between them increases in regards to Penny's training for her new job at Bernadette's company.
Wolowitz feels really nervous when NASA asks him to throw out the first pitch at a Los Angeles Angels game. Leonard and Penny attempt to show Sheldon he is wrong after he says that he and Amy are a "superior couple."
Penny receives the cold shoulder from Raj's girlfriend after he tells her some information about their past history. The boys think about buying into Stuart's comic-book emporium.
After the guys decide to have a physicist's retreat, the girls head to Las Vegas for the weekend.
Penny receives a company car from the pharmaceutical company where she's now employed but has trouble coming up with the money to pay back Leonard for the one he bought for her. Meanwhile, Sheldon and Raj look at a potential research grant.
Songs: Merle Travis -- Dark as a Dungeon
At her new job, Penny has a client who develops a crush on her. It turns out that he is a middle-aged version of Howard Wolowitz. Amy and Bernadette argue over a photo shoot of female scientists.
Amy, Bernadette, and Penny decide to re-enact their high school proms with their respective fellows. Raj, Emily, and Stuart are included too.
Sheldon panics when Leonard goes into the hospital for an operation. Meanwhile, Raj learns that his parents have gotten a divorce.
Sheldon retires his Fun With Flags You Tube series, while Leonard, Howard, and Raj look through the papers of a deceased colleague and Bernadette discovers what her boss really thinks of her.
Amy fixes a traditional Victorian Era Christmas Eve dinner whose guest list includes Raj's newly separated father, visiting from India.
Songs: Covered by Bernadette -- Here Comes Santa Claus, Covered by Leonard, Howard, and Raj -- Jingle Bells
Raj is concerned over whether a probe he designed will work in outer space. Penny and Amy coerce Leonard and Sheldon into taking them shopping.
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?"
Songs: Johnny Galecki, Kaley Cuoco -- Soft Kitty