The Big Bang Theory (season 4)

At dinner, Howard demonstrates a robotic arm that he "borrowed" from the Jet Propulsion Laboratory by unpacking dinner. Later at home, he uses the arm as a massager and even tries to use it to masturbate, but executes the wrong program and gets his genitals stuck to the arm, forcing him to call Leonard and Raj for help. They take him to the hospital (along with the arm and Howard's laptop containing the program for the arm movement) where the nurse turns off the laptop, which releases the arm's grip on Howard's genitals. Later Howard calls Leonard, saying it "happened again", indicating that he again tried to use the arm to masturbate and got his genitals stuck for the second time.

Meanwhile, Penny comes to know of Sheldon's new friend Amy and is shocked when Sheldon announces his plans to conceive a child with her via in-vitro fertilization based on their superior genetics using Penny as a surrogate. Penny suggests that he should first go out with Amy on a date. Since Sheldon cannot drive, and because the date was Penny's idea, she is forced into giving Sheldon a ride and ends up chaperoning. During the drive and at the restaurant where they are having dinner, Penny tries to make Sheldon and Amy have a proper conversation, as it is a first date for each of them. All her attempts fail and to add to her annoyance, Sheldon calculates the number of dates that Penny has had in her life, and the number of sexual partners she has had. Amy then asks Penny whether she ever felt like a "slut". Penny denies it, but appears unsure. When Sheldon and Penny return home later that night, Penny, who is still upset with Sheldon's claim that she had sex with 31 men, threatens to tell his mother about his procreation plans, causing him to drop them.

Recurring characters: Mayim Bialik as Amy Farrah Fowler, Vernee Watson as Althea, and Carol Ann Susi as Mrs. Wolowitz
Note: This was the most watched episode of season 4, with 14.04 million viewers.

Sheldon's estimate for his life expectancy leads him to the conclusion that he will miss by only a few years "the singularity, when man will be able to transfer his consciousness into machines and achieve immortality". He therefore changes his diet by eating cruciferous vegetables instead of pizza on Thursdays and decides to go jogging with Penny in the mornings in hopes of extending his life expectancy. Due to the diet of cruciferous vegetables he has a bad case of flatulence and he tumbles down the stairs while going down for his jog, Sheldon builds a robotic replication of himself which he calls a "Mobile Virtual Presence Device" (the telepresence robot by Willow Garage^[4]) that would go through all the hazards of life that Sheldon would otherwise have to endure, while he stays behind in a "secure, undisclosed location" (his bedroom). The guys dismiss the MVPD as a stunt (Penny calls it Shel-Bot). Leonard then goes over to Sheldon's room to convince him to drop the idea, but Sheldon refuses to listen to him and proceeds to cite Section 74C of the Roommate Agreement requiring Leonard to assist him (by providing him transportation) "in the event one of the roommates becomes a robot". Leonard reluctantly takes the MVPD to work, completely regretting it after the MVPD continuously irritates him during the drive. Later Leonard takes the MVPD to the Cheesecake Factory for dinner. Sheldon, from his bedroom, spots Steve Wozniak having dinner there and sends the MVPD over to his table, telling him that he has a 1977 Apple II. Wozniak says that if Sheldon had the Apple II there he would sign it. Sheldon then takes the Apple II and rushes out of his apartment, but trips and falls down the stairs, breaking the Apple II and his ankle. The episode ends with a now bedridden Sheldon using the MVPD to force Penny to sing "Soft Kitty" to him.

Guest star: Steve Wozniak as himself

Sheldon and Amy are very compatible with each other, as evidenced by how well they can play "counter-factuals", a game they invented requiring them to know what the other is thinking when answering a question about "an alternate world that differs from ours in one key aspect" (Leonard fails miserably when he attempts to play this game). However, Amy's presence does not go down well with the other guys, who already find it difficult to handle Sheldon himself, and they start hanging out at Penny's apartment to escape "ShAmy" (the name the guys and Penny gave for the couple). But one day at lunch, Amy belittles Sheldon's occupation as a theoretical physicist relative to, in her opinion, her superior occupation of neurobiology, prompting Sheldon to terminate their friendship. Following the breakup (or according to Sheldon, "our friendship outlived its utility"), Sheldon adopts 25 cats as a substitute for Amy. A worried Leonard calls Sheldon's mother, who rushes over to the apartment. She calls over Amy and, using reverse psychology, she makes Sheldon offer to reconcile with Amy, which she agrees to after a negotiation on the amount of responsibility Sheldon has to accept for the breakup. The episode ends with Sheldon and Amy giving away $20 to anybody willing to adopt a cat.

Recurring characters: Mayim Bialik as Amy Farrah Fowler and Laurie Metcalf as Mary Cooper

The guys run into Howard's ex-girlfriend Bernadette while having dinner at the Cheesecake Factory. Though Howard hides under the table when he sees Bernadette, the incident nonetheless reignites his feelings for her. He seeks help from Penny, who agrees on the condition that he reveal the reason behind his breakup. He confesses that Bernadette caught him engaging in cybersex with a fellow World of Warcraft player, who is later revealed to be one of Howard's male colleagues at Caltech. Howard and Bernadette later meet at the Cheesecake Factory and after Howard reveals the reason he indulged in cybersex (he thought that Bernadette was not interested in having sex with him), they make amends and decide to give their relationship another try. They go out on a date, following which they make out in Bernadette's car.

Meanwhile, Sheldon and Raj argue over the latter wanting a desk in their office, with Sheldon citing budgetary reasons (saving money for a drawer full of Red Vines, a marshmallow shooting rifle, and a super executive ant farm with glow-in-the-dark sand) for not providing a desk. Raj offers to buy his own desk, to which he reluctantly agrees. When he enters his office later, he sees Raj sitting on a huge and ornate desk which takes up half the office space. After Raj refuses to obey Sheldon's subsequent order that he remove the desk, a series of annoying confrontations (Sheldon calls it "tit-for-tat" exchanges) ensues between the two. Eventually, Sheldon prepares ammonia and hydrogen sulfide to create a bad smell in order to throw out Raj from their office, which Raj tries to counter by lighting his cinnamon-apple-scented aromatherapy candles. However this makes the gases ignite, causing an explosion.

Recurring character: Carol Ann Susi as Mrs. Wolowitz
Guest stars: Katee Sackhoff as herself and George Takei as himself
Note: Melissa Rauch became part of the main cast in this episode.

When Amy decides to introduce Sheldon to her mother, he becomes worried as being introduced to Amy's mother would indicate that Amy wants to be his girlfriend. So he begins to avoid Amy, removing all possible contact with her and even disguising himself so that she would not recognize him. However Amy catches Sheldon outside the apartment building and then tells him that she only wants to introduce him to her mother so that she would be convinced that Amy is in a relationship and leave her alone. Later when talking to Amy's mother on webcam, a now relieved Sheldon and Amy lie to Amy's mother that they are in a "sexual relationship", which does not go too well with her.

Meanwhile, as Howard now has a girlfriend, Leonard decides to invoke the "Girlfriend Pact" (from the Season 3 episode The Creepy Candy Coating Corollary) with Howard. Howard and Bernadette set up a double date with Leonard and one of Bernadette's friends, Joy. Joy behaves in an obnoxious and inappropriate manner during the date, which disgusts Leonard. However he later accepts another date with Joy due to understanding that sex is a strong possibility.

Recurring characters: Mayim Bialik as Amy Farrah Fowler, Kevin Sussman as Stuart Bloom and Carol Ann Susi as Mrs. Wolowitz
Guest stars: Charlotte Newhouse as Joy and Annie O'Donnell as Mrs. Fowler
Note: Kaley Cuoco is absent from this episode due to a broken leg sustained during a real life horseback riding accident. This is the first time that a regular cast member has not appeared in an episode.

Raj's younger sister Priya, a lawyer by profession, visits Pasadena en route to Toronto. Though unknown to the others including Raj, Priya had been involved in a sexual encounter with Leonard five years earlier, despite Leonard's assurance to Howard that he would never hit on Priya in deference to Raj. That night, Priya sneaks into Leonard and Sheldon's apartment unknown to Sheldon and has sex with Leonard. Sheldon finds out the following morning that Leonard and Priya had "coitus" and frames an elaborate, flawless lie to cover it up, which involves Leonard having had sex with an imaginary Irish bartender named Maggie McGeary. But Leonard decides not to hide the truth and confesses to Raj that he slept with Priya. Raj is initially upset, but reconciles with Leonard after he says that Priya broke his heart. The guys then unleash confessions of all of the deceptions they have perpetrated on each other, including Howard dropping Raj's iPhone into a urinal, Sheldon's experiment feeding moth parts to Leonard mixed in his food and Raj using Sheldon's toothbrush. Sheldon becomes upset at Raj for using his toothbrush and terminates his friendship with him, but immediately forgives him after Raj reveals that he gave him a talking Thomas the Tank Engine with real puffing smoke for Thanksgiving.

Recurring character: Aarti Mann as Priya Koothrappali
Note: Kaley Cuoco was absent from this episode due to a broken leg sustained during a real life horseback riding accident.

Howard needs top-level security clearance to work on a government surveillance satellite, so the FBI sends Agent Angela Paige to interview Leonard, Sheldon and Raj in order to do a background check on him. None of the guys are able to convince Agent Paige that Howard is trustworthy; Raj fears being deported back to India, while Leonard unsuccessfully tries to ask her out by seeming "confident". Sheldon on the other hand, unwittingly tells her that Howard crashed the Mars Rover (from the Season 2 episode The Lizard Spock Expansion). As a result, Howard is denied clearance. Sheldon feels guilty that he caused Howard's career to be set back and apologizes to Howard, who refuses to accept it. Later when Sheldon discusses the issue with Penny, Penny refers to an incident from Star Trek (where Captain Kirk won the Kobayashi Maru by reprogramming the simulator), which inspires Sheldon to use neurolinguistic programming to modify Howard's thoughts to force him to accept his apology. That too does not work, so as a last resort, Sheldon offers Howard his spot on the couch. Howard is touched at this gesture and forgives Sheldon. The episode ends with Sheldon taking back his spot after only 94 seconds.

Guest stars: Eliza Dushku as FBI Agent Angela Paige and Neil deGrasse Tyson as himself
Note: Because of her broken leg, Kaley Cuoco is shown working as a bartender, instead of in her normal job as a waitress at The Cheesecake Factory.

The guys decide to go to a special midnight screening of Raiders of the Lost Ark which has 21 seconds of unseen footage. However when they arrive at the theater, they are made to wait in a long queue, making Sheldon whine about how Leonard, Howard and Raj wasted time by having dinner. Later Wil Wheaton arrives and is immediately allowed entry without having to stand in a queue due to his celebrity status, which angers an already-impatient Sheldon. Eventually the guys are barred from watching the movie as the theatre is fully occupied. Just as the four are about to leave, Sheldon discovers a side door and enters it. Leonard, Howard and Raj follow Sheldon and find him holding some film cans, having stolen the reels of the movie in retribution for being denied from watching the movie. Wheaton too finds Sheldon holding the movie reels, leading to a mob of angry Raiders (and Wheaton) chasing the four from the theater, mimicking the opening scene of Raiders of the Lost Ark.

Meanwhile, Amy decides to spend the evening with Penny and Bernadette, who are planning a "girls' night", despite her initially planning to go with the guys to Raiders of the Lost Ark. As Amy had never been to a girls' night before, she grosses out Penny and Bernadette with descriptions about her female parts as she thinks that is what girls talk about and looks up Wikipedia to determine sleepover customs, which Penny and Bernadette reluctantly go along with. During Truth or Dare, Amy and Bernadette get on Penny's case about Leonard. Annoyed, Penny storms off to her bedroom. Later Amy finds out that girls engage in lesbianism during sleepovers and enters Penny's bedroom. The episode ends with a horrified reaction from Penny, indicating that Amy may possibly be trying to indulge in lesbian sex with her.

Recurring characters: Wil Wheaton as himself and Eric Andre as Joey
Note: Mayim Bialik became part of the main cast in this episode.

Penny informs Leonard that her father Wyatt has come on a visit and asks him to pretend that they are back together as he is the only boyfriend she had that her father ever approved of. He is initially wary of the idea, but gleefully plays along to get her to confess (he also calls her out on her hypocrisy at being mad at him for going along with her stupid, flawed plan), which she does when he is Wii fishing with her father. Penny's father confronts her about the hoax and admonishes her for always being dishonest to him. After Penny goes to her room, her father pleads with Leonard to get back together with her because he does not want her to go back to dating boyfriends whose personalities he does not approve of and wants grandchildren who do not grow up in a mobile home. Leonard then plays along as Wyatt pretends to angrily throw him out of Penny's apartment.

Meanwhile, Howard and Raj decide to spend the night in a control room so that Raj can control a ground-based telescope located in Hawaii in the hope of seeing the star Epsilon Eridani dim, which would be evidence of a planet orbiting it. Raj becomes angry when Howard invites Bernadette until he discovers that Bernadette brought wine. A drunk Raj complains that no girl wants to kiss him, to which Bernadette shows sympathy for him. At this, Raj attempts to kiss her, but ends up kissing Howard when he attempts to stop Raj from kissing his girlfriend. The next day, Howard and Raj act awkward around each other and lash out at Leonard and Sheldon when they enquire about what they had seen on the telescope.

Elsewhere, Sheldon thinks that Leonard and Penny have got back together (he is unaware they are faking it). So he modifies the Roommate Agreement to include a Penny-specific section which addresses some of Penny's annoying habits, which if she does while at their apartment, would cause Leonard to pay a fine to Sheldon. When Leonard tells him later that he and Penny "broke up" again, a frustrated Sheldon throws the agreement papers into the air and yells whether Leonard even thinks of other people.

Guest star: Keith Carradine as Wyatt
Note: Penny's father's name is changed from the second season episode, "The Maternal Capacitance" when Penny referred to him as "Bob". However, in this episode, his name is Wyatt.

While on a girls' night out with Penny and Bernadette, Amy meets Penny's ex-boyfriend Zack and immediately becomes attracted to him. She later discusses her symptoms with Sheldon (elevated heart rate, moist palms, dry mouth, vascular throbbing in the ears and genitalia and saying an involuntary "hoo" in Zack's presence) and comes to the reluctant conclusion that she is sexually aroused by Zack. It is also pointed out that Sheldon might be jealous. Sheldon prefers to assume that Amy has contracted an alien parasite. Later when Sheldon discusses about Amy and Zack with Penny, Penny tells him that there is "something" he could do about Amy's "urges", but as usual he misunderstands what Penny is trying to say to him (Penny meant that Sheldon should show romantic feelings to Amy) and instead tries to bring Amy and Zack together. He manages to contact the right Zack Johnson and sets him up on a date with Amy at a bar. This proves to be a failure, as Amy finds out that Zack is extremely stupid. Later while walking home with Sheldon, Amy does something she never did before- she holds Sheldon's hand. When Sheldon asks why Amy is holding his hand, Amy says it is just an experiment, but then lets go and says, "Nope. Nothing. Never mind.", indicating that she is not attracted by Sheldon's appearance, yet chose Sheldon's intellect over Zack's looks.

Meanwhile, after one of the scientists at the biology lab is bitten by a radioactive rat, Howard and Raj argue about who would be the better superhero (with Raj expressing his desire to be "Rat-Man"). Knowing that Raj is afraid of spiders, Howard proposes a contest where the first person who dares to put his hand into a jar with a huge spider in it and keeps it there for the longest time gets to be the superhero. This however backfires, as the spider crawls onto Howard's arm, freaking him out. The duo decide to settle their argument once and for all by having a wrestling match, but this too fails as instead of wrestling each other, they only end up circling and insulting each other.

Recurring character: Brian Thomas Smith as Zack Johnson

Penny gets back together with Zack. The guys insult Zack's low intelligence which upsets him; however he reconciles with the four after Sheldon offers him Milk Duds and he accompanies them to the comic book store, where Stuart announces the New Year's Eve costume party. The guys decide to come as the Justice League of America and also decide to include Penny as Wonder Woman (who initially refuses, but later agrees) and Zack as Superman (because according to Howard, "he is the only person we know with actual muscles"). Leonard dresses up as Green Lantern, Sheldon as The Flash, Howard as Batman and a reluctant Raj as Aquaman. Sheldon forces Penny to wear a black wig, as Wonder Woman has black hair, but Penny refuses to wear the wig and decides not to come to the costume party. Sheldon, Howard and even Zack are unable to convince Penny to change her mind. Later when Leonard talks to her in an attempt to convince her to come to the party, Penny reveals that she got back together with Zack only because she did not want to spend New Year's Eve alone. She confesses that she'd rather go to a regular party with Zack than to a costume party with Leonard. Leonard questions why not him, prompting Penny to change her mind and put on the wig. At the comic book store, the group win the award for the Best Group Costume. The episode concludes with the six witnessing an ongoing car theft and then scurrying off despite wearing Justice League costumes.

Recurring characters: Brian Thomas Smith as Zack Johnson and Kevin Sussman as Stuart Bloom

Leonard gets an idea to develop a smartphone app that will allow users to solve differential equations just by taking a picture of them. However, Sheldon catches the heat from Leonard when he tries to put himself in charge despite the app being Leonard's idea (Sheldon had named himself as the chief executive, financial, and operating officers among other high-rank positions while listing Leonard as only the founder). Despite eventually acknowledging Leonard as the leader of the project, Sheldon continually criticizes Leonard's leadership in the development of the app. After Sheldon suggests names for the app that have his name in it (the "Surprisingly Helpful Equation-Linked Differential Optimized Numerator", which has "Sheldon" as its acronym, and "Project NodlehS", which has "Sheldon" spelled backwards), Leonard tells him to stop. Sheldon abruptly calls for a vote to change the team's leadership, resulting in Leonard kicking Sheldon off the team. After unsuccessfully trying to bribe Howard and Raj to dump Leonard and join his "rival company", Sheldon resorts to sabotaging Leonard's project by playing a theremin while they work, and Leonard kicks him out of the apartment in retaliation. When Penny sees Sheldon moping on the stairs, she sympathetically invites him to her apartment for a cup of cocoa, but quickly regrets her decision. She asks the guys to take Sheldon back, promising that he will apologize. Sheldon initially refuses to apologize, so Penny tells him to use sarcasm to disguise his lack of sincerity, an idea to which Sheldon immediately takes a liking. The guys agree to put him back on the team, but Sheldon quickly goes back to criticizing their work, demanding that they completely start over. The episode ends with Sheldon, having been kicked off the team again, reluctantly working with Penny on an app she mentioned to him while sitting on the stairs- the app identifies shoes and finds out where to buy them.

Amy asks Penny to join her, Bernadette and the other guys on a trip to a science conference in Big Sur, California, as she believes them to be her best friends. At first she rejects the offer, but then accepts after learning about the free spa treatment. Before they leave, Sheldon ("travel supervisor") explains the timetable and seating arrangements. Amy convinces Sheldon to let Penny ride in the lead car with themselves and Leonard because her "Nebraska backwoods skills" could help them if their car breaks down. During the trip, Penny gets sent to the second car with Howard, Raj and Bernadette after she attempts to stand up to Sheldon. At the hotel, Bernadette spots Glenn, her professor at college and ex-boyfriend, a tall handsome guy who intimidates Howard. When Howard confronts Bernadette over Glenn, she gets mad at him and decides to stay with Amy and Penny. Since there are only two beds and Penny cannot sleep because of Amy's nightmares (which cause her to bite), Penny moves out of her room and asks Leonard if she can stay with him and Sheldon. Leonard accepts, but after Penny tells him that they aren't going to have sex, Sheldon wakes up, asking them if they are not going to have "coitus". As he receives different answers (Penny says "yes", Leonard says "no"), Sheldon leaves and seeks shelter in Raj's room, where Raj is about to watch Bridget Jones's Diary. Sheldon eventually kicks out Raj, who then goes to Leonard and Penny's room, just when they are about to have sex. He crawls into the bed vacated by Sheldon, stopping Leonard and Penny from having sex. The next morning as Sheldon, Leonard, Howard, Raj, Bernadette and Amy sit on a panel, with Penny in the audience, they all exchange (initially thinly veiled) criticisms at one another stemming from the previous night's events. An irritated Penny then accepts a ride back to Pasadena with Glenn, much to Leonard's horror. Later while returning home, Leonard gets pursued by the police for speeding as he is distracted by the thought of Penny being with Glenn.

Guest star: Rick Fox as Glenn

Sheldon guest lectures at a university, but his teaching style is considered boring and intolerable, and results in negative online feedback from his students. On Amy's advice, he decides to take acting lessons from Penny for $40 to learn how to more easily communicate with his students, though his attitude during the lessons frustrates Penny. Finally, they act out a Star Trek fanfiction script which Sheldon wrote in his childhood, in which Mr. Spock takes a young Sheldon to the 23rd century to bring hope and peace to the galaxy. Penny plays the role of Spock as she feels that Sheldon needs to come out of his comfort zone, while Sheldon plays the dual role of himself and his mother. However while acting out the script, Sheldon immerses himself so deeply in the part that he is brought to tears, because he does not want to be taken away from his mother by Spock. Penny then calls his mother and gives the phone to Sheldon so that his mother can console him.

Meanwhile, Raj develops a crush on Bernadette after she comforts him over not having female company. He starts daydreaming various scenarios involving him and Bernadette; the first one is Howard asking him to satisfy Bernadette's sexual needs while he is away on a fellowship in Israel; the second one is a dying Howard, who has met with a fatal accident, asking him to take care of Bernadette and satisfy her sexually after his death; the third and final one has him and Bernadette dancing Bollywood-style.

President Siebert invites the guys to a fundraiser for Caltech that Saturday. While Leonard, Howard and Raj are willing to attend, Sheldon refuses to go and stays back in the apartment; however, he changes his mind after a video chat with Amy, who tells him that if he is not at the fundraiser, the task of raising funds for the physics department would fall to Leonard and Raj, whom, according to her, would probably fail in raising funds, as a result of which the funds would go to departments like geology and liberal arts; but during the fundraiser, he insults many donors by refusing to shake hands with them due to his mysophobia as a result of which the physics department loses potential donors. At the fundraiser, the guys are introduced to Mrs. Latham, an elderly philanthropist whose condescending attitude terrifies them, but she later tells Leonard that she likes making smart people nervous. She then invites Leonard to dinner the following night to talk more about his research, despite none of the guys (including Leonard) feeling like they did anything right at the fundraiser. During dinner, she reveals that she is willing to donate money to the physics department on one condition- Leonard must have sex with her. Leonard is not comfortable with this and is unwilling to prostitute himself, despite Sheldon's plea that he do it for the physics department. The next night, Leonard again has dinner with Mrs. Latham, during which she tells Leonard that whether he has sex with her or not, she will donate to the physics department. After this, she flirts with him, eventually causing him to give in and have sex with her. The next morning, Penny and Sheldon catch him as he arrives home after his "walk of shame" and tease him slightly. Later at work, he is applauded by everyone at Caltech, including Howard, Raj and President Siebert for his "gigolo work" which brought funds to the physics department.

Recurring character: Joshua Malina as President Siebert
Guest star: Jessica Walter as Mrs. Latham
Note: Johnny Galecki was nominated for the Primetime Emmy Award for Outstanding Lead Actor in a Comedy Series at the 63rd Primetime Emmy Awards for this episode.

Bernadette is upset because Howard always goes home after sex so that he can help his mother in the morning. She insists that Howard moves in with her, which Howard is not interested in until he has a big fight with his mother after reaching home regarding his sexual activity with Bernadette. After spending the rest of the night in Leonard and Sheldon's apartment, Howard moves out of his house to Bernadette's apartment. Both are happy initially, but later Bernadette realises that Howard is too dependent on his mother and insists that he should not expect the same treatment from her. As a result, Howard returns home, where his mother (who did not know that Howard had moved out) grounds him for "running away".

Meanwhile, after Howard offhandedly mentions that Raj's younger sister Priya has come to Pasadena and is staying at Raj's apartment, Leonard rushes over there to talk to her. Leonard and Priya then decide to pursue a long-term relationship much to Raj's indignance, who even quotes from the Manusmriti to dissaude Priya from dating Leonard, only for Priya to remind him that he eats beef which is also forbidden in the Manusmriti. Amy, who considers Penny her BFF, rushes over to Penny's apartment to console her when she hears the news, but Penny insists that she is not upset that Leonard and Priya are dating. Later while having dinner, Penny finds out that Priya, being a lawyer, is much more successful than her and also sees that Leonard (and even Amy) is crazy about Priya's achievements. After returning to her apartment following dinner, Penny breaks down crying, which confirms that she still has feelings for Leonard. Amy, who is also in Penny's apartment, comforts her before using electrodes to determine which brain regions are active during crying, as she plans to make a rhesus monkey cry by stimulating the analogous areas of its brain. During the weekend, with Leonard and Priya having gone to Santa Catalina Island, Howard grounded by his mother and Raj at home in strong disapproval of Leonard and Priya dating, Penny spends her time with Sheldon and Amy (via webcam), who tells her that thanks to her contribution, she was successfully able to make a rhesus monkey cry.

Recurring characters: Aarti Mann as Priya Koothrappali and Carol Ann Susi as Mrs. Wolowitz

Now Leonard and Priya are dating and since she lives with Raj, Leonard and Howard decide to have dinner there instead of the normal venue which disturbs Sheldon who prefers their place. Sheldon leaves and stops by the Cheesecake Factory where Penny tells him he has to accept that the gang will be hanging out at Raj's place more often. Amy tells him that Leonard is the nucleus of their social group and not Sheldon. As a result, he sets up a new group consisting of Kripke, Stuart, Zack and LeVar Burton (whom he tweeted) with him as the nucleus. Sheldon's plans are dismissed by the others in favor of Zack's dating stories and getting drunk and singing karaoke. Naturally, Sheldon does not like that very much, so he decides to go back to his old friends, who, in the meantime, realized that they actually missed Sheldon. In the end, LeVar Burton finally does show up at Sheldon's place, but when he sees Kripke, Stuart and Zack singing karaoke together, he leaves immediately, stating "I am so done with Twitter".

Meanwhile, Bernadette and Amy want to take Penny out dancing to get her mind off of Leonard and Priya. She agrees to come with them on the grounds that they stop pestering her about Leonard and Priya. As she changes clothes, she tells the girls that it is the first time in her life she is satisfied with being single and does not want to have sex with a random guy to make up for it, however when Amy finds the snowflake that Leonard gave to her after his expedition to the North Pole, she changes her mind as her feelings for Leonard come back to the surface again.

Recurring characters: Aarti Mann as Priya Koothrappali, Kevin Sussman as Stuart Bloom, John Ross Bowie as Barry Kripke, and Brian Thomas Smith as Zack Johnson
Guest star: LeVar Burton as himself

Priya has begun to dominate in her relationship with Leonard, buying him new clothes and forcing him to wear contact lenses (which Leonard is not comfortable with). She also feels threatened by Leonard continuing to hang out with Penny, even though they have broken up, so during sex, she tells him to break all contact with Penny. Leonard initially hesitates, but still tries to tell Penny to stay away from him, albeit indirectly, with an obscure anecdote about Charles Darwin's finches. Penny does not get the right message, but Leonard takes comfort in the fact that he tried. Later Penny interrupts Leonard's date with Priya and is completely oblivious to what is going on. Leonard once again indirectly tries to tell Penny to stay away from him, but this time Penny gets the message and realizing that Priya was behind this, decides to break all contact with Leonard. Leonard immediately attempts to go after his ex-girlfriend, only to crash into the doorframe due to his uncomfortable new contact lenses.

Meanwhile, Howard shows Sheldon, Raj and Penny a card trick in which a volunteer picks a card and after shuffling the deck, Howard tells the volunteer his/her card. Raj and Penny both try out the trick and are amazed by it. Though at first his attitude is dismissive, Sheldon eventually becomes obsessed with discovering the trick's secret, as even Penny could figure it out. He goes to the extent of using a barcode reader and even hacking the Oak Ridge National Laboratory's Cray supercomputer, attempting to procure Uranium 235 on Craigslist in order to recreate the trick. It is then revealed (to the audience) that the card trick is just a prank played by Howard, Raj and Penny on Sheldon. Raj and Penny willingly pretended that Howard was successful, knowing fully well that Sheldon would go nuts trying to figure out the trick's secret. When Sheldon wants Howard to perform the trick on him in the end, Raj manages to get a peek on Sheldon's card and uses hand signals to tell Howard the right answer. Sheldon is puzzled once more, still not knowing that he had been pranked all along, while Howard and Raj both laugh gleefully.

Recurring character: Aarti Mann as Priya Koothrappali

Sheldon's World of Warcraft account has been hacked and all of his WoW stuff have been stolen. He enlists the help of the other guys in finding the hacker. Howard manages to trace the hacker and reveals that his name is Todd Zarnecki and lives in Carlsbad. The guys then drive to Carlsbad to get back Sheldon's WoW stuff. At Todd's home however, not only does Todd refuse to return Sheldon's stuff, but he also takes away Sheldon's Klingon Bat'leth. Defeated, the guys decide to return home, but their car breaks down midway, prompting Leonard to call Penny to fetch them. When Penny hears their story, she drives them back to Todd's house where she delivers a kick to Todd's groin and forces him to return Sheldon's stuff.

Meanwhile, Amy, Bernadette and Penny criticise Priya and her arrogant, dominating behavior, with Amy going to the extent of asking Bernadette and Penny to "throw their waste" at Priya. Penny takes Amy's comments lightly, but after an encounter with Priya in the apartment lobby, she agrees with Amy.

Recurring characters: Aarti Mann as Priya Koothrappali and Carol Ann Susi as Mrs. Wolowitz
Guest stars: Christopher Douglas Reed as Todd and Lanny Joon as Officer Shin

Penny spreads a rumor that Bernadette is thinking of breaking up with Howard. Amy tells Sheldon, who tells Leonard, who tells Priya, who later tells Raj. Priya informs Leonard that Raj has a crush on Bernadette and even writes poems about her. When Raj hears the rumor from Priya, he gets excited, as he could finally have his own shot with Bernadette. Howard is completely unaware of the rumor and plans to ask Bernadette to marry him. The others try to stop him from asking, as they believe that Bernadette will reject him and he will become blindsided, except Raj, who selfishly encourages Howard to go through with his plan in the hope that Bernadette will reject him. When having dinner one night, Howard pulls out the proposal ring, as he cannot imagine a better time to ask her than with all of his friends around. Despite the protest of the others, he gets on his knees and starts to talk. At that moment, Bernadette cuts him off in what appears to be a rejection, however she actually accepts his marriage proposal, devastating Raj.

The rumor about Bernadette breaking up with Howard motivates Amy and Sheldon to conduct an experiment in which they concurrently spread two false rumors: a "tantalizing" one (Sheldon and Amy had sex) and a "non-tantalizing" one (Amy decided to start a herb garden) to see which rumor gets back to them first. Amy starts both rumors by informing Penny and, as expected, the rumor about the two having sex reaches the entire group in under 24 hours while the other one is not mentioned again. When Howard's proposal distracts the group from the rumor, they decide to start over with their experiment. Amy visits Penny (who just got a text from Bernadette informing her about the proposal) again and tells her that she is getting orthotics and that she is pregnant with Sheldon's baby. Moments later Leonard meets Amy in the hall after he receives a text message from Penny, informing him about the false pregnancy. He confronts Amy, who, in return, just wonders "is there anything on there about orthotics?".

Physicist Brian Greene makes a cameo appearance at the beginning of this episode, featuring his book The Hidden Reality.

Recurring characters: Aarti Mann as Priya Koothrappali, Brian George as Dr. V.M. Koothrappali, and Alice Amter as Mrs. Koothrappali
Guest star: Brian Greene as himself

When Leonard takes a shower with Priya while Sheldon experiences an event of force majeure, he gets charged with two violations of the roommate agreement (Leonard denied access to the bathroom when Sheldon had to urinate and Leonard was not the only person in the shower). 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 (which Sheldon does not like at all) on pizza night, Sheldon seeks shelter at Penny's, who invites him to join her on a girls' night out with Amy and Bernadette. After the girls have some cocktails and Sheldon mentions he had learned to dance at cotillion balls as a child, they decide to take Sheldon dancing. After dancing, Sheldon takes an intoxicated Amy back to her apartment. Amy tells Sheldon not to give in to Priya's law skills, just like a monkey would defend his territory. She then proceeds to kiss him and then rushes to her bathroom to vomit. The next day, Sheldon presents an overhauled version of the roommate agreement to Leonard and asks him to sign it. When Leonard shows his reluctance, Sheldon activates a "self-destruct sequence" on his laptop; If Leonard does not sign the agreement within a minute, an e-mail will be sent to Priya's parents informing them of their relationship. Leonard accuses Sheldon of bluffing and blackmailing and does not see any harm in Priya's parents knowing. Priya, however, knowing that her parents do not approve her dating an American, tells Leonard their relationship is over if he does not sign the new agreement. After a failed attempt to cut the power supply from Sheldon's laptop, Leonard gives in and Sheldon aborts the program. Later that day, Sheldon speaks with a hungover Amy via webcam and thanks her for the advice that she gave him the night before. They agree to treat their relationship like a "crashed computer" and "restore" it to the last point it worked for both, thus deciding to forget about the entire evening's events. Meanwhile, Leonard, not knowing how strict Priya's parents are, argues with her about whether or not she is ashamed of him.

Recurring character: Aarti Mann as Priya Koothrappali
Guest stars: Arnold Chun as Ho-Jun, Jeff Blum as Waiter, and Tom Yi as Dispatcher
Note: Jim Parsons won the Primetime Emmy Award for Outstanding Lead Actor in a Comedy Series for this episode.

While shoe-shopping with Penny and Amy, Bernadette reveals that Howard and her have been invited to a double date by Priya. Amy suspects that Priya is trying to win over the weakest member of their social group, just as a cheetah attacks the weakest specimen in a herd of wildebeests. Therefore, she proposes to use Bernadette to spy on Priya and spread disinformation about Penny and Leonard. Bernadette is uncomfortable with lying, as she went to a catholic school, but nonetheless goes along with the plan. When the four meet for dinner, Priya makes a snide remark about Penny's acting career. Penny and Amy order Bernadette to tell Priya and the others that Penny is on her way to Prague for a movie part and that she is dating an architect (although this is AutoCorrected to astronaut). Priya, Leonard and Howard begin to ask questions about this news (being very interested in details about where Penny met the astronaut), to which Bernadette has to improvise answers, increasingly unnerving and frustrating her. Bernadette excuses herself to the bathroom and calls Amy to tell her that the lie (as well as her calm) is unraveling. She also reveals that Priya and Leonard are planning a trip to India to meet the Koothrapallis. Consequently, Penny wants her to find out if the two are getting engaged. Bernadette finally snaps and storms out, leaving Priya and Leonard befuddled.

Meanwhile, Raj, who is still very lonely and does not want to be the "fifth wheel" during the double date, visits Sheldon in his apartment. He tries to get advice about whether or not he should try to cure his social anxiety using an experimental drug, however Sheldon is preoccupied with his "three-person chess" project, as he does not only adapt the popular game for 3 players with a new board design, but also adds new chess pieces. Sheldon finally advises Raj to do so and accompanies him to a coffee shop to observe the drug's effectiveness. It ends up working very well, as Raj starts to talk to a woman named Angela, who also seems to like him. However, an adverse effect begins to manifest itself, causing Raj to lose all his inhibitions and strip completely naked, thus scaring off Angela. In the end, Sheldon, Leonard and Howard play a test game of Sheldon's chess version, to which he added a multitude of new chess pieces and rules while a still-nude Raj is watching them.

Recurring character: Aarti Mann as Priya Koothrappali
Guest stars: Tiffany Dupont as Angela and Whitney Avalon as Elsie

While dining at the Cheesecake Factory, Bernadette and Howard reveal that their parents have not been informed about their engagement yet. Howard arranges a lunch for his fiancé and his mother and they end up getting along well. After Howard hears the good news while talking to his mother, who is in the bathroom, he decides to make the move and tell her about the engagement. To his horror, she collapses from an apparent heart attack. Howard takes her to the hospital as fast as he can. When the others hear about this, they rush to the hospital. Sheldon, being extremely mysophobic, is initially reluctant to visit the hospital and only agrees to come after Penny pressures him to go. When Bernadette finds out that Howard was telling his mother about his engagement before she collapsed, she is very upset, as she believes that she is the reason all this happened. When Mrs. Wolowitz finally wakes up, the doctor informs them that it had not been a heart attack and that she wants to see Bernadette before anyone else. It is revealed that she actually had food poisoning from the restaurant she and Bernadette ate at and was worried about Bernadette's well-being, whom she actually likes a lot. Bernadette ends up being very mad at Howard, as he led her to believe that it was all her fault.

While in the hospital, Priya and Penny start searching for the cafeteria and bond in the process. They mainly discuss Leonard's skills in the bedroom. Sheldon has other things to worry about, as he tries to avoid contact with anything in the hospital and, when he has to go to the restroom, is trapped in there, waiting for someone to open the door for him. When he tries to avoid a coughing patient on the way back, he seeks shelter in a random room. Much to his horror, it turns out to be a bio-hazard room, where he is exposed to a deadly disease. Sheldon is eventually forced to stay in the hospital under a 2-week quarantine after the exposure, with his friends keeping him company in hazmat suits.

Recurring characters: Aarti Mann as Priya Koothrappali and Carol Ann Susi as Mrs. Wolowitz
Guest stars: Phil Abrams as Dr. Bernstein and Sharon Omi as Nurse
Continuity Error: In 3 episodes (The Adhesive Duck Deficiency, The Vartabedian Conundrum aired prior to this episode, and The Werewolf Transformation aired subsequent to this episode) Sheldon visited hospitals without displaying the reluctance and discomfort he had in this episode. Indeed, Sheldon has discussed with Dr. Stephanie Barnett and Dr. Beverly Hofstadter his fondness for hospitals.

Bernadette announces that her dissertation has been accepted, earning her a Ph.D. and a well-paid job, Later Bernadette decides to buy Howard an expensive Rolex watch as a present and tells him to "let her worry about the money", a comment that disturbs Howard. Meanwhile, Leonard's and Priya's noisy sexual encounters sends Raj to spend the night at Sheldon's apartment. When Leonard finds him in his bed, he proposes that Raj moves in with Sheldon until Priya finds her own place. Raj likes the idea, signs Sheldon's roommate paperwork and moves in with him. He then prepares a fancy dinner for them which delights Sheldon who decides Raj is a much better roommate than Leonard. Penny stops by, stays for dinner and the both of them get drunk from the wine Raj served. Penny confesses to Raj that she "screwed up", as she should not have broken up with Leonard, and that she would be "on" him (Raj) if they were not friends. Priya receives a video call, Leonard overhears that she is moving back to India and storms out revealing their relationship to her parents.

At the end of the episode, Sheldon discovers Leonard sleeping on their couch, just before Howard shows up and announces that he had a fight with Bernadette over the watch. Penny wakes up and is horrified when she notices Raj in Leonard's bed beside her. She tells him that last night never happened and tries to sneak out of the apartment; however, they are busted by the others. Penny just states that "it's not what it looks like" and leaves. Sheldon then asks "What does it look like?"

Recurring characters: Aarti Mann as Priya Koothrappali, Brian George as Dr. V.M. Koothrappali, Alice Amter as Mrs. Koothrappali, and Carol Ann Susi as Mrs. Wolowitz