List of The Big Bang Theory episodes (season 5)

Raj finds himself in hot water with Leonard and Howard after supposedly sleeping with Penny and the latter discovering his fantasies about Bernadette (who also became angry at Raj because of his fantasies, and now has to contend with Howard's feeling of distrust of her as a result). Raj and Penny later talk and it turns out they didn't sleep together because Raj ejaculated prematurely when Penny tries to help him put on his "Protection". Nonetheless, Penny feels that this has damaged her relationship with the guys permanently and decides to move back to Nebraska, as she has not had any worthwhile acting jobs since moving to Pasadena. When she comes over to apologize and announce her intention to move, she gets a call from her manager, informing her that she got a part in a hemorrhoids commercial, prompting her to scrap her plans.

Meanwhile, Sheldon has appointed himself the captain of the guys' paintball team. When they are at another of the university's tournaments where they fight against other departments, their team falls apart because of Leonard, Howard and Raj's lack of enthusiasm due to everything that has gone on with Penny. Sheldon, blaming himself, puts down his paintball gun and walks outside, proclaiming that geology isn't a real science. Following that, he is promptly shot several times. Leonard, Howard, and Raj immediately rush out to avenge Sheldon's "sacrifice" and even manage to claim the victory for the physics department.

Recurring character: Christine Baranski as Dr. Beverly Hofstader

Priya has returned to India and she and Leonard are attempting a long-distance relationship. Their first time having cybersex is ruined when Leonard's screen freezes. Leonard then takes advice from Howard on how to maintain such a relationship and then prepares to perform one of the things he taught him, but is humiliated to learn that Priya's parents are sitting beside her.

Meanwhile, Penny picks up a new chair, which at first Sheldon thoroughly likes until he finds out that she picked it up off the curb. He begins to harass Penny to dispose of it, resulting in many rejections. Sheldon then enlists Amy to try and coax Penny to get rid of it. However, Penny catches on and tells Amy to leave. Amy, fearing her friendship with Penny is over, sits on the chair to show her loyalty. She is then bitten by something moving in the chair, causing her and Penny to flee the apartment. Penny then tosses the chair, but Howard and Raj find it and bring it up to Leonard and Sheldon's apartment, as Raj doesn't want to sit on the floor all the time. Unbeknownst to them, the strange creature is seen moving again while they carry the chair up to the apartment.

Recurring characters: Aarti Mann as Priya Koothrappali, Brian George and Alice Amter as Dr. and Mrs. Koothrappali

Amy asks Leonard to accompany her to a friend's wedding as Sheldon is too immature to accompany her. At the last wedding they attended, he behaved like a child (and now is also occupied with his affection for model trains). When they are at the wedding, Leonard gets depressed, as he is reminded of Priya. Amy eventually cheers him up by telling him that her boyfriend is at home playing with model trains. Eventually, she convinces Leonard, who, according to himself, "is not much of a dancer", to go dancing with her (Amy's dancing skills have been shown in the episode "The Agreement Dissection"). He gets into it and at last finds himself able to have a good time, though he ends up pulling a muscle in his groin. Amy eases his pain by breaking the head off of a nearby swan ice sculpture and giving it to him, so he can cool his injury. When they come back, Leonard thanks her and, after inviting her in for tea, gives her a kiss on the cheek, which Amy believes is a clear sign of him falling in love with her. She immediately asks Penny for advice and then decides to send Leonard an email to tell him that she is not into him. Leonard describes the evening to Sheldon, who has become obsessed with smaller and smaller model railroad scales, as they are more fun. He inadvertently makes it sound like he and Amy had sex when mentioning that he had pulled his groin, prompting an unexpected jealous reaction from Sheldon, who hits him and tells him that "she is not for you!".

Bernadette becomes upset again when she and Howard start discussing where they are going to live in the future. Howard expresses his desire to have her move in with him and his mother, as Howard is accustomed to his mother doing all the work (an obligation that Bernadette rejected in the episode "The Cohabitation Formulation"). She is initially reluctant, but agrees to spend a weekend at Howard's house later for the purpose of trying the idea. She feels very uncomfortable during the stay, as Mrs. Wolowitz is very intrusive and doesn't give them any privacy. Furthermore, Howard acts childishly and even has his meat cut by his mother. The next morning, Bernadette and Mrs. Wolowitz make breakfast for Howard. When she brings it to his bed, she mentions that communication with his mother is tricky as they are "very different people". When she talks to Mrs. Wolowitz she also shouts and sounds just like her. In the end, Howard complains about having to cut his pancakes himself.

After playing Dungeons & Dragons with the others, Sheldon decides to let the game's dice make trivial decisions for him from now on, so his mind is freed up for other, more important things. Although his theory proves useful as he is being able to complete two important research papers very quickly and is "close to figuring out why the LHC has yet to isolate the Higgs boson", he ends up having to eat things he wouldn't normally eat and even grows a moustache.

Meanwhile, Penny sets Raj up with her deaf friend, Emily (Katie Leclerc), for whom his selective mutism is no longer an issue. He immediately takes a liking to her, although he requires Howard as a communicator at first. The two continue to see each other and Raj learns sign language to be able to talk to her on his own. After Howard tells Penny that he buys her all kinds of expensive things (such as diamond earrings) and even leased her an expensive car, they begin to suspect Emily is taking advantage of Raj. Sheldon, who is revealed to be a notary public and has helped Raj on several occasions with his banking documents, tells them that he is actually much wealthier than he lets on, stating that the Koothrappalis are "about halfway between Bruce Wayne and Scrooge McDuck". Unable to reason with Raj or Emily, Penny informs Raj's parents about his girlfriend, who then threaten to cut off his allowance if he does not break up with her. Raj tells them that he chooses love and then informs Emily about his decision and also tells her that they are going to have to return her car and all the jewellery he bought for her (including a very expensive necklace from Cartier). Emily then dumps him and leaves a heartbroken Raj behind. He then commiserates at the Cheesecake Factory with his friends. When Penny brings the bill, they leave him behind with it, as they now know just how much money he has. In addition, Penny tells him that he better not cheap out on the tip.

Recurring characters: Brian George and Alice Amter as Dr. and Mrs. Koothrappali

Sheldon and Leonard pay another visit to the comic book store and decide to start a fantasy sword collection by buying a sword replica from a prop that was used in Game of Thrones (the sword being Longclaw, first of House Mormont then belonging to Jon Snow). After Leonard finishes bargaining over the price with Stuart, Wil Wheaton, one of Sheldon's over 60 sworn "mortal enemies", shows up and invites Stuart and the guys to a party at his place. Leonard accepts the invitation and is fully intending to go, an act that alienates Sheldon, who then begins treating Leonard after the principle of Schrödinger's cat: he is a friend and an enemy to him at the same time until he knows whether or not Leonard goes to the party. When Leonard is about to leave on the night of the party, he gets a text from Stuart, informing him that Brent Spiner is a guest. At first, Sheldon rejects the offer to come along, despite being a big fan, however, at last shows up to "fight for our friendship" and to meet Brent Spiner. Wil Wheaton is genuinely pleased to see Sheldon has made it and gives him a signed in-the-box original Wesley Crusher action figure as an apology for missing the Jackson, Mississippi convention that made Sheldon hate him so many years ago, supposedly ending his feud with him. After reading what Wil wrote, Sheldon declares him his friend and even hugs him. At that moment, Brent Spiner shows up and takes the action figure out of its box, deeply upsetting Sheldon, who immediately places Spiner on his list of mortal enemies. Leonard then bargains with Spiner for two signed action figures of Commander Data. They settle at $30 and the promise that he will come to Leonard's birthday party.

Meanwhile, Howard is ecstatic when his design for a "deep field space telescope" is accepted by NASA, which also requires him to travel up to the International Space Station as a Payload Specialist. As the Space Shuttle program has been decommissioned, he will have to travel in a Russian Soyuz rocket, which is launched from Kazakhstan. Upon hearing this, Bernadette's excitement turns into worry about the safety of the Soyuz rocket. She is also upset that Howard didn't tell her before making this important decision. When Howard tries to be a good boyfriend by pretending to start over with his decision making to include his fiancée in it, Bernadette promptly forbids him to go, causing Howard to get mad at her. While they are in bed, Bernadette pretends to have changed her mind and when they are about to have sex, she tells Howard that she has to go brush her teeth before. Moments later, it is revealed that Bernadette told Mrs. Wolowitz about Howard's plans, who is heard turning down the idea immediately. Howard is so angry at Bernadette's betrayal that he tells her to leave in the middle of the night. When with the girls the next day, she asks them if she she has been acting selfish and realizes that she is the one who needs to apologize (Amy refers to her action as "despicable"). Bernadette then apologizes to Howard and he forgives her. While they are kissing, Mrs. Wolowitz is heard again, making it clear that Howard's "tuchis is not leaving this planet!".

Recurring character: Wil Wheaton as himself
Notable guest stars: Brent Spiner as himself

Sheldon's mother, Mary (Laurie Metcalf), has come to visit from her home in Texas. He is excited and plans to get her to cook some of his favorite food and attend a lecture of 2011 Nobel Prize laureate Saul Perlmutter with him. Leonard offers instead to take her out to dinner. Mrs. Cooper also opts to go sightseeing with the group rather than visiting the lecture with her son. Sheldon becomes jealous and is angry that she is ignoring him and doesn't cater to his demands. After an argument with his mother, he takes Amy to the lecture. After they come back to Amy's apartment, she informs him that, while he is a genius, his emotional reactions to his mother's ignoring him are no different from that of any other human being. Amy also points out that the less intelligent might be able to handle their emotions better by not overthinking them. Sheldon, after sitting out in the rain, returns home soaked and with a bad cold, prompting his mother to immediately ignore the others and focus on him. When he is in bed and once again demands that she sings "Soft Kitty" to him, they are interrupted by Leonard halfway through the song. Sheldon then makes her start over, causing his mother to regret once again that she didn't take Sheldon to a "follow-up" sanity test with a psychiatric specialist in Houston many years ago.

Recurring character: Laurie Metcalf as Mary Cooper

A successful Halloween prank from the group enrages Sheldon, who promptly starts working on his revenge. His efforts all end up being fruitless, as Sheldon makes his pranks too obvious to the others by behaving oddly. Leonard reverses his prank on him, while Raj is delighted by the snake Sheldon puts into his desk drawer. He finally seems to have succeeded in tricking Howard with an electric handshake. When Howard breaks down because of a heart condition, Sheldon is terrified. Bernadette orders him to inject adrenaline into Howard's heart. After doing so, he is astonished to find out that it all was a ruse by Howard and Bernadette. Sheldon then ends up shocking himself while wondering how he could have fallen for that.

Meanwhile, Leonard meets a good-looking girl called Alice (Courtney Ford) at the comic book store who also happens to be a comic book enthusiast. She gives him her phone number to discuss trading comic books and they end up kissing while at the apartment. Leonard finds himself in a dilemma, as he can either be a "good guy" and stay loyal to Priya or a "bad guy" and have an affair with Alice. A discussion with Penny doesn't help, and after Sheldon makes him feel less guilty by citing Friedrich Nietzsche, Leonard decides to go to Alice's apartment. While they are making out, he changes his mind and confesses that he has a girlfriend, prompting Alice to throw him out immediately. At the end of the episode, Leonard video calls Priya and tells her about Alice. Priya is seemingly okay with it, prompting Leonard to become suspicious. When he asks her about it, Priya reveals that she also cheated on him, as she had sex with her ex-boyfriend a couple of weeks ago. Leonard is upset and ends the call early. At that moment, Sheldon leaps out from under the couch cushions in zombie face paint, scaring Leonard. He triumphantly shouts "Bazinga, punk! Now we're even!".

Recurring characters: Aarti Mann as Priya Koothrappali, Kevin Sussman as Stuart

The girls are trying to pick out dresses for Bernadette's and Howard's wedding and seem to have trouble with it. Amy becomes heartbroken when Howard mentions a text message from Bernadette with a bridesmaid dress she likes, as she discovers that Bernadette and Penny went trying on dresses without her. Later, Sheldon tries to contact Amy numerous times using social networks like Twitter and Facebook and, after Leonard suggests it, the telephone. She does not answer to any of his messages, so Leonard takes Sheldon over to her house to check if she is okay. When they arrive at her apartment and hear her sobbing, Leonard leaves, stating that "I'm single, I don't need this crap", suggesting that he has ended his relationship with Priya (although there has so far been no other reference to this). Amy tells Sheldon that she didn't answer to any of his messages because she wanted to be alone and professes how upset she is about the girls excluding her. She asks for them to engage in one night of coitus and, after bargaining over what they are going to do (including Sheldon suggesting that he pat her head and say "who's a good Amy" or a neck rub and Amy suggesting French kissing), they finally settle on cuddling. Sheldon, not liking this experience at all, tells Leonard and Howard angrily to "get their women in line" the next day, as he doesn't have time to comfort Amy and already missed the opportunity to continue his work on string theory and to start building his Lego Death Star. When the guys inform Penny and Bernadette, they feel guilty and later attempt to apologize, however Amy refuses to forgive them. That night Leonard and Sheldon pick up a drunk Amy from the parking lot of a liquor store. She tells them that she has been drinking wine to drown her sorrows, just like Penny taught her, and calls Sheldon "cuddles", much to his embarrassment. She also tries to persuade him to take her to the motel across the street and "have his way with her". They take her home, and, the next day, Penny and Bernadette try to apologize to her again. Bernadette finally succeeds by asking Amy to be her maid of honor, which she accepts full of joy because of all the wedding work to come (including Bernadette's bridal shower and bachelorette party). The episode ends with Amy taking a video of them trying on dresses together.

Leonard accepts an offer to go to the movies with Penny, strictly as friends. However, when she chooses a Jennifer Aniston movie to watch, Leonard takes issue, and reveals that he only pretended to like things during their relationship in the hope of getting sex at the end. As sex is now off the table, he is no longer going to pretend to want to watch what she wants to watch, and insists on watching a documentary about a South American dam project, and also forces her to pay for her ticket. He does a similar thing at a bar afterwards, but Penny responds by talking to a nerdy young man writing a film script, since it is "not a date." Leonard attempts to show her up by talking to a woman at a nearby table as well. However, the young man Penny was speaking to leaves, and she tries to start hanging out with Leonard again. They end up saying some embarrassing things about each other, culminating in Leonard revealing Penny cannot even spell "asthma." When they get home, Penny reveals that she was actually liking Leonard's tougher and more dominating streak, and he puts it back on when he realises he may get sex after all, but blows it at the last moment by reverting to his more timid personality.

Meanwhile, Sheldon, who suffers from ornithophobia, is upset when a large Black-throated Magpie-Jay (incorrectly identified as a Blue Jay on screen) sets up a nest on the apartment windowsill, and tries to fend it off with cat impressions. Throughout the night, the bird won't leave, and Sheldon's increasingly unusual efforts to get rid of it—including building a ultrasound noise generating machine—aren't helping, and eventually result in the bird flying into the apartment and perching on his spot. Desperate, he calls Amy and Bernadette in, and they encourage him to try and take the opportunity to overcome his ornithophobia. After an initially hesitant approach, he not only overcomes his ornithophobia, but becomes smitten by the bird, nicknaming it "Lovey Dovey" and wanting to keep it as a pet. The girls are less than enthused; Bernadette observes it is likely someone else's pet, and Amy is clearly upset that "you need hollow bones to get some sugar around here." But when Sheldon opens the window to get the bird's nest, it flies out, devastating him. After putting up pictures around the apartment building with a caption "Have You Seen This Bird?", he reveals that the bird had laid an egg in its nest, of which he is going to take care.

While at the comic book store, Stuart is introduced to Amy, who accompanies the guys and is revealed to be bored by comic books. Stuart immediately develops a crush on her and proceeds to ask Leonard about the current state of Sheldon and Amy's relationship. He then gets Leonard to check if Sheldon is fine with him asking her out. Sheldon depicts the scenario as moot, assuming that a renowned neurobiologist like Amy would never be interested in a guy like Stuart anyway. When Leonard and Sheldon return to the comic book store, they meet Dale, who replaces Stuart while Stuart is out having coffee with a girl. Sheldon, knowing that the girl must be Amy, conceals his true feelings and repeatedly states that he doesn't care, although actions like friending Stuart on Facebook (despite having disapproved of the site before) to spy on him and asking Penny out on a date to make Amy jealous suggest otherwise. After talking to Penny, he interrupts Amy and Stuart during a movie to change the paradigm of their relationship. He hesitantly asks Amy to be his girlfriend, which she gladly accepts. When Sheldon presents her a "relationship agreement", she is delighted and calls it very romantic. Amy later feels that she should've gotten a lawyer, when she finds out that her obligations as a girlfriend include taking care of her boyfriend's injuries. But nevertheless, they continue their relationship as boyfriend and girlfriend.

Meanwhile, the guys find out that a new expansion pack for Mystic Warlords of Ka'a called "Wild West and Witches" has come out, which they initially turn down because of its theme and the price, but eventually buy after an argument about who would win in a fight between Billy the Kid and the Wizard of the North. Leonard also tries to return the new Mystic Warlords of Ka'a expansion pack, but Raj goes out to buy the "deluxe limited edition" of the pack in a collector's tin. Leonard once again turns it down, but then ends up buying it, while being furious at himself for doing so.

Recurring character: Kevin Sussman as Stuart

Leonard is contacted by Jimmy Speckerman (Lance Barber), a former high-school classmate who bullied him on a regular basis, with a potential business proposition. Leonard, initially hesitant, decides to go along with it in order to confront Speckerman. When they do meet, Speckerman greets Leonard like an old friend, seemingly oblivious to Leonard's discomfort, and proposes his idea—glasses that turn all movies into 3D. Sheldon, fed up with Leonard's refusal to confront Speckerman, immediately attacks him for his bullying ways, presenting him with a list Leonard drafted of all the things Speckerman did to him, and the gang leave. Speckerman is shocked to read the list. Later on, he turns up at the apartment drunk and weepy, begging Leonard's forgiveness and saying that he "wins." The next morning, however, a hungover Speckerman reverts to his old bullying ways and begins to insult Leonard again, leading an angry Leonard to order him out of his apartment. Leonard ends up shoving Speckerman, who is enraged and chases Leonard and Sheldon out of their own apartment.

Meanwhile, Amy and Bernadette, while hanging out in Penny's apartment, discuss their own trouble with bullies. Penny, however, absent-mindedly mentions having pranked a girl who got good grades by tying her up and leaving her in a cornfield, revealing that she was a bully herself. Realizing this, she feels awful and tries to make amends by calling the people she bullied to apologize. When she is coldly rebuffed in the attempt, Amy suggests that she could make herself feel better by doing something altruistic. After declining to serve soup or build houses for the poor, she finally agrees to donate some of her clothes, as they only take up her space. When she throws her clothes in the container, she discovers a large pile of second-hand clothes she likes and immediately begins helping herself, much to Bernadette's dismay and Amy's excitement. The next evening, while at the Clothes Bank, collecting more donated clothes, Penny suddenly realises the immorality of what she is doing, and they leave. Bernadette, however, runs back to collect a pair of shoes she liked, justifying her actions by the fact that she works at a soup kitchen.