The Big Bang Theory (season 3)

The men return home from their three-month expedition at the Magnetic North Pole (from the Season 2 finale), and Penny finally reveals her feelings for Leonard by kissing him as soon as he visits her. Meanwhile, Howard and Raj reveal to Sheldon that they and Leonard tampered with his experiment on magnetic monopoles by using an electric can opener. Sheldon is angry as he had already submitted his results to the university, and is forced to make an apology, making him the butt of jokes from everyone at the university, particularly Kripke. Feeling betrayed, Sheldon returns to his home in Galveston, Texas. On Penny's advice, Leonard, Howard and Raj reluctantly go to Galveston to bring him back. At his home, Sheldon becomes increasingly annoyed with his mother's strict Christian lifestyle. When the guys come over and plead with Sheldon to come back to Pasadena, he initially refuses, but following an argument with his mother about evolution, he forgives them and returns to Pasadena. Penny and Leonard then finally have sex, but both of them now feel their relationship got weird.

Leonard and Penny struggle to recover from a not-so-great first hookup and try to figure how to overcome it. A romantic evening between the pair soon turns into a night filled with drunken sickness. The next day Penny talks to Sheldon and Sheldon points out that if things do not work out, they can always return to being friends. After Sheldon tells Leonard that he spoke to Penny, Leonard goes to Penny's apartment. Penny tells Leonard that being friends was much simpler and that it will take the pressure off, something that Leonard agrees to. They decide to go back to being friends, however they quickly give in and resume their relationship. Meanwhile, Sheldon and Howard stake their most valuable comic books (Sheldon's "Flash of Two Worlds" against Howard's Fantastic Four #48) on a bet to determine the species of a cricket after they hear it chirping. Sheldon claims it is a snowy tree cricket, but Howard insists it is a common field cricket. Along with Raj, the three spend a long time locating the cricket. They settle the bet by taking "Toby" to Professor Crawley, Caltech's depressed entomologist, who has just lost funding for his lab. Howard is proven correct that it is a common field cricket, so Sheldon has to give up his copy of The Flash.

After a sexual encounter that results in Penny's bed breaking, Penny and Leonard sleep in Leonard's room, much to Sheldon's dismay. Sheldon tries to condition Penny using chocolate, despite Leonard's opposition, rewarding her for what he considers to be correct behavior. Meanwhile, Howard and Raj go out to a goth club and meet two girls. After they say they would prefer to go "somewhere else and have some fun," the four end up in a tattoo shop, which makes Raj and Howard reveal their true selves and admit to not being goths, missing their opportunity with the girls rather than getting tattoos.

Raj's research on trans-Neptunian objects comes to a dead end and he faces deportation to India unless he gets a new job. After he unsuccessfully applies for other jobs at the university, Sheldon offers Raj a chance to work "for" him, rather than "with" him. Raj reluctantly accepts Sheldon's offer. Later, Sheldon and Raj disagree on how to solve a work-related problem and Raj walks out. Sheldon apologizes to Raj after realising he was right (but does not concede to him being wrong), and they agree to continue working together. With Raj working for Sheldon, Howard feels lonely, so he tries to hang out with Leonard and Penny (even making them breakfast). They tell him that they need to be alone together, but feel guilty and bring him back.

Leonard reluctantly agrees to fulfill a pledge he made to Howard years earlier and asks Penny to set Howard up with one of her friends. Penny introduces Howard to her friend Bernadette and they go on a double-date. It firstly seems like they have nothing in common, but they start to bond when they learn about each others' problems with their mothers. Meanwhile, Sheldon enters a collectible card game tournament after he hears that Wil Wheaton, for whom he harbors a deep resentment for missing a 1995 Sci-Fi convention, is also participating. With Raj as his partner, they reach the final match against Wil and Stuart. Just as Sheldon closes in on victory, Wil lies, claiming his grandmother's death prevented him from appearing at the convention, which touches Sheldon's heart. Sheldon allows Wil to win, but Wil then admits to lying, leaving Sheldon even more resentful.

Note: This episode marks the first appearance of future regular cast member Melissa Rauch as Bernadette Rostenkowski and also marks the first cameo appearance of Wil Wheaton on the show.

Penny invites her friends over to her apartment to watch the Nebraska Cornhuskers football game that Saturday, but does not invite Leonard as he is not a football fan. Determined to fit in with his girlfriend's friends, Leonard learns the rules of football from Sheldon, who is highly knowledgeable about football having grown up in football-crazy Texas. Using the knowledge, Leonard goes over on Saturday to watch the game, but his comments are too clinical and he fails to fit in with Penny's friends. He later becomes bored and leaves at half-time to fly kites with Sheldon. Meanwhile, Howard upsets Raj after abandoning him during a kite fight with Leonard and Sheldon to pursue a girl and causing them to lose. Howard decides to make it up to Raj by spending an entire Saturday with him at the La Brea Tar Pits, but fails to keep his promise and again abandons Raj at the tar pits to pursue another girl.

When Penny invites her guitarist ex-boyfriend Justin over to sleep on her couch, Leonard becomes upset. They start a fierce argument, which makes Sheldon, reminded of memories of his parents fighting, upset. He tries to convince Penny to make up with Leonard, but ends up telling her how Leonard dislikes her temper, which only makes her angrier. Upset with the constant bickering between the two, Sheldon leaves his and Leonard's apartment. Sheldon tries to take refuge in Raj's apartment, but sees him arguing with his parents over webcam. He then goes to Howard's house, but hears him arguing with his mother. Leonard and Penny begin to search for Sheldon and eventually find him at the comic book store. They manage to convince Sheldon to come back to the apartment, but not before allowing him to buy a robot and a comic book. Justin ends up sleeping on the couch in Leonard and Sheldon's apartment (with Sheldon sitting in his spot) and Leonard and Penny, having finally made up, sleep together in Penny's apartment.

Sheldon hears Penny crying for help after slipping in her shower and dislocating her shoulder. Sheldon is forced to help her dress and drive her to the hospital emergency room, despite not having driven a car before. Sheldon drives slowly and annoys Penny at the hospital, but Penny successfully receives aid. Also under the influence of strong analgesics, Penny forces Sheldon to sing Soft Kitty to her while helping her into bed. Meanwhile, Leonard, Raj and Howard go on a camping trip to watch the Leonid meteor shower, but all succumb to the effects of "magic" cookies given to them by Deadhead campers nearby. Raj, Howard and even Leonard make fun of Leonard's American accent while looking at the stars. They then share a conversation about their secrets; Raj talks about what it would be like to be king of the rabbits, Leonard thinks of changing his name to "Angelo", and Howard admits that he lost his virginity to his second cousin. The trio begin to run out of food, but Howard remembers that his mother packed food for him and shares it with Leonard and Raj. The trio then succumb to the effects of munchies and forget about the meteor shower, with Leonard and Raj making fun of Howard's experience with his second cousin.

After their third date, Bernadette asks Howard where their relationship is going. Howard avoids her for a week, thinking about whether he should "settle" for her or hold out for the dream of superstars like Megan Fox. After a dream in his tub involving a romantic-evening-turned-lecture from Katee Sackhoff, he decides that he should stick with reality. Howard proposes to Bernadette at The Cheesecake Factory, but gets rejected. In order to win back her affections, he then sings her his version of the song "Bernadette" (by the Four Tops), and succeeds when she declares it the most romantic thing anyone has ever done for her. Meanwhile, Kripke severely embarrasses Sheldon on National Public Radio's talk show Science Friday by filling Sheldon's office with helium so that his voice is higher-pitched than usual. While at first pouting and accepting defeat, Sheldon is convinced by Leonard and Raj (who originally enjoyed the prank) to fight back. Sheldon takes revenge on Kripke by setting off gooey foam into Kripke's office, but the trick backfires when the visiting Caltech president and board of directors are also hit. Sheldon gives himself away with a pre-recorded video stating that he has sent the taped trick to YouTube, and proclaims himself the mastermind, also giving Leonard and Raj away.

Bernadette joins the guys and Penny for dinner and shows an interest in physics, particularly in Leonard's work. Leonard offers her the chance to tour his lab and watch him conduct an experiment. Howard becomes jealous and accuses Leonard of trying to steal Bernadette's heart from him. After Leonard texts Bernadette that Howard has become jealous, Bernadette storms out before having sex with Howard, accusing him of trying to control whom she takes an interest in. Howard apologises to Bernadette the following day as she arrives to watch Leonard's experiment, and they kiss and make up. Meanwhile, Penny, jealous over the fact she cannot talk to Leonard about his job, asks Sheldon to teach her physics. After teaching her, Penny ends up spouting off a prepared spiel Sheldon taught her while the group has dinner.

At Christmas, Leonard's mother visits, much to Leonard's horror and Sheldon's delight. Penny becomes upset after Leonard failed to tell her about his mother's visit, (nor his mother about their relationship), and the problem gets worse when Leonard learns that Sheldon has been in touch with his mother. Leonard is told about his parents' pending divorce, his mother's surgery, and the death of his dog, all of which Sheldon had known for weeks. Beverly questions Howard and Raj about what she views as their ersatz homosexual relationship (alluding to her last visit in The Maternal Capacitance), goes out drinking with Penny, and shares a passionate kiss with Sheldon when she returns to the apartment (which they later agree to keep secret from Leonard), though she remarks that she would prefer the busboy she met at The Cheesecake Factory.

Leonard and Penny go on a double-date with Howard and Bernadette, but when Penny reveals that she has taken career advice from a psychic, Leonard laughs, infuriating her. Howard tells Leonard that he will have to accept that people have differing beliefs if he wants to maintain a relationship, so Leonard apologizes to Penny and agrees to visit her psychic, despite her having declined to read a book debunking psychics. Meanwhile, Sheldon and Raj attend a university mixer, with Sheldon as Raj's wingman after Raj bribes him with a Limited Edition Green Lantern lantern. They meet Abby, who takes a liking to Raj, and her friend Martha, who tries to connect with Sheldon. The four play Rock Band at Sheldon's place for a first date. For a second date, Raj bribes Sheldon with his pair of Hulk hands, signed by Stan Lee. After Sheldon announces that he is going to bed, Martha asks if she can stay in his room to avoid Raj and Abby, who are "getting busy". Sheldon obliges, but immediately leaves to sleep in Leonard's room, leaving Martha alone.

Leonard and Sheldon return from dinner to find their apartment broken into and their TV, laptop, hard drives, video game consoles and video games stolen. Sheldon fears being alone in the apartment after the robbery, so he forces Leonard and Penny to stay with him. The next day, Howard designs a state-of-the-art security system for the apartment using components he "borrowed" from the Department of Defense. After Sheldon gets caught in the security system, he decides that the apartment is no longer safe and plans to leave Pasadena for a safer city. After rejecting Enid, Oklahoma, Boone, North Carolina and the entire state of Nebraska (because Penny is from there), he decides to move to Bozeman, Montana. But when Sheldon arrives there, he gets robbed again, so he returns to Pasadena.

Sheldon's search for the answer to a physics problem keeps him up for several days and he becomes obsessed with finding the answer. His obsession leads him to visualize food as atoms and even sneak out in the middle of the night to go to the mall ball pit. He then decides that he needs a menial job to think better since Albert Einstein came up with the Theory of Relativity while working at a menial job at the Swiss patent office. Since the United States Patent and Trademark Office is near Washington DC, and he does not want to move out of Pasadena, Sheldon interviews for any menial job with the County of Los Angeles. At the county office, Sheldon angers the woman interviewing him and security remove him. Sheldon then decides to work at the Cheesecake Factory with Penny as he considers her job the most menial of all. He works as a busboy and waiter without actually being hired or demanding pay, and turns out to be a more efficient waiter than Penny until he drops and breaks a tray of dishes. The scattering of the shattered pieces leads him to the answer to his problem, and he promptly walks out without cleaning up the mess. Meanwhile, Leonard, Penny, Howard and Bernadette go to disco night at the roller skating rink. Raj is left out as he does not have a girlfriend, but later successfully pressures Howard to take him to the skating rink as it was his idea.

Leonard announces to the guys that a professor is unable to attend a conference in Switzerland and visit CERN's Large Hadron Collider, so he has been designated to be his replacement, and gets to take one guest with him. Sheldon wants to go, but Leonard decides to take Penny as the trip would coincide with Valentine's Day, their first together as a couple. Sheldon is distraught and begins to constantly give signs indicating that Leonard "betrayed" him. He gives Leonard breakfast in bed to change his mind, but Leonard is firm on taking Penny. Sheldon later convinces Penny to drop out of the trip, but this does not go down well with Leonard, who terminates their friendship. Later that night, Penny falls ill, so Leonard asks Sheldon to accompany him to Switzerland in Penny's place, but Sheldon also falls ill, having hugged Penny and been given the bug. As a result, Raj accompanies Leonard to Switzerland while Sheldon and Penny spend Valentine's Day together.

Stuart announces that Stan Lee is coming to the comic book store on Thursday to sign comic books, much to the guys' excitement. However, Sheldon cannot attend as he has to appear in court after running a red light while driving Penny to the hospital in the episode "The Adhesive Duck Deficiency". At court, Sheldon insults the judge and is imprisoned as a result. Sheldon later apologizes to the judge and is freed, but falls out with Penny since she made him miss meeting Stan Lee. To make it up to him, Penny takes Sheldon to Stan Lee's house to meet him, but Stan, not impressed by their intrusion, sarcastically invites them in. Sheldon, not understanding sarcasm, enters Stan's house, causing him to call the police. In the end, Sheldon gleefully returns to his apartment with a restraining order from Stan and hangs it next to his restraining order from Leonard Nimoy.

The guys return to the apartment with a large box of TV and movie collectibles from a garage sale, including a prop version of the One Ring. This turns out to be a prop made for The Lord of the Rings film trilogy, with high value to collectors, and the four promptly argue over who gets to keep it. Leonard eventually gives it to Penny for safekeeping. Sheldon sneaks into Leonard's room (where Penny is sleeping) and tries to steal the ring, but she wakes up and punches Sheldon. The next day in the cafeteria, the guys all grab onto the ring and decide whoever is the last one holding the ring will get to keep it. Leonard removes himself from contention when Penny shows him the contents of a bag she got from Victoria's Secret. Sheldon, Raj and Howard then all fall asleep and let go of the ring. The next morning, Leonard says he sent it back to the original owner, but actually kept it hidden in his room. That night, Sheldon tries to take the ring again and he and Leonard wrestle for it on Leonard's bed. Penny walks out of the room and mutters to herself about how she should "go back to dating dumb guys from the gym."

Sheldon is delighted when he wins a science award, but is terrified of accepting it because of his fear of speaking to a public audience. Leonard, Raj and Penny offer to help Sheldon overcome his fear, with Sheldon christening himself, Leonard, Raj and Penny as the C-Men (Cooper-Men), but all the C-Men fail to overcome Sheldon's fear; Raj tries to teach Sheldon meditation to calm his nerves, but Sheldon instead imagines a Godzilla-like monster approaching his simulated city Sheldonopolis; Penny takes Sheldon to buy a new suit to give him confidence, but Sheldon is more interested in weird and fancy suits; Leonard attempts a psychotherapy session with Sheldon, but Leonard actually ends up having a nervous breakdown after reminiscing a humiliating incident with his mother. As a last-ditch solution, Penny offers Sheldon alcohol. This solution actually works, but it makes Sheldon drunk and he speaks nonsense during the awards ceremony. At one point in his speech, Sheldon drunkenly removes his pants. When Sheldon wakes up the next morning, unaware of the events which happened the previous night, he sees his humiliating speech uploaded on YouTube.

After having sex, Leonard says "I love you" to Penny, but she only replies "Thank you", prompting both of them to start thinking about where their relationship is heading. The next night, Penny and the guys have a bowling match with Stuart and some of the comic book store regulars (with the loser to be publicly humiliated in a fashion to be chosen by the victor). As one member of Stuart's team could not make it, Stuart substitutes him with Wil Wheaton, with Sheldon vowing revenge for what Wheaton did to him in The Creepy Candy Coating Corollary. During the match, Leonard offers Penny chili cheese fries, to which she expresses her love of chili cheese fries. Angry that Penny could describe her feelings for food but not for him, Leonard starts a fierce argument with her, following which she leaves the bowling alley in a huff. Without Penny, the guys are forced to forfeit the match. The next day, Sheldon makes Leonard and Penny supposedly patch things up and then schedules a rematch that night. During the match, Wheaton tells Penny that he endured two years of misery with a girlfriend who could not say "I love you" to him. When Penny goes to bowl, she feels pressured by Leonard's encouragement and lashes out at him. Realizing that she cannot say "I love you" to Leonard, she breaks up with him and storms out of the bowling alley again. The guys again have to forfeit the match, and Wheaton reveals to Sheldon that he intentionally broke up the couple so that his team would win. In the end, the guys have to enter the comic book store dressed up as female superheroes under Stuart's idea of humiliating them for losing the match.

Leonard and Penny have broken up and are no longer talking to each other. Sheldon continues to maintain contact with Penny and goes over for a spaghetti dinner at her apartment. Howard tells Sheldon that he cannot be friends with both Penny and Leonard, but Sheldon has dinner with both the guys and Penny. Unable to keep his friendship with her secret, he reveals to Leonard that he is still friends with Penny, which Leonard does not mind. The next day, Penny bumps into Leonard in the laundry room and tells him that she is taking Sheldon with her to Disneyland that Saturday. When she drops Sheldon home late on Saturday night and puts him to bed, she tells Leonard that they can remain friends despite their break up, which he accepts. However, he suggests that they have a friends with benefits relationship, which she refuses.

Dr. Elizabeth Plimpton, a cosmological physicist from Princeton University, accepts Sheldon's invitation to stay over at the apartment during her visit to Caltech. However, she instead takes an immediate interest in Leonard, and the two end up sleeping together. The next morning, Penny learns about their tryst and becomes jealous. Leonard assumes that he and Elizabeth are now an item and shows her around, introducing her to Raj and Howard. Later that night, Howard and Leonard go to Raj's apartment for Halo night and find Elizabeth (trying to seduce Raj). When she sees Howard and Leonard as well, she suggests role-playing sex with all three of them, much to the shock of the men. Raj manages to lock the other two out of the apartment so he could be alone with Elizabeth. Back home, Leonard and Penny discuss whether or not he needs to explain to Penny what happened. Although Penny keeps insisting that he does not, Leonard explains that he had sex with Elizabeth because "she let [him]".

Leonard fights with Sheldon over the setting of the thermostat before storming out of the apartment and visiting Penny, who had been listening to the argument. He then proceeds to tell Penny about how he met Sheldon back in 2003. Sheldon's departing former roommate and Louie/Louise (the transvestite male then occupying the apartment that Penny moves into in the first episode) meets Leonard and both warn him that Sheldon is "crazy". Having found the apartment, Leonard meets Sheldon whom, at the door, questions Leonard about the sixth noble gas (Radon) and "Kirk or Picard?" before allowing him to enter. Leonard goes to sit down, but learns about the acquisition of the lawn chair, which Sheldon calls "my spot". Leonard then undergoes further examination, and the ensuing rigorous interview questions and intrusive conditions suggest Sheldon's literalness, rigidity, egotism, and peculiar priorities. Another flashback, introduced by Penny wondering why Leonard continues to live with Sheldon, reveals two events: Sheldon inadvertently kept Leonard from revealing a top secret rocket fuel to his girlfriend at-the-time Joyce Kim, a North Korean spy, angering her so much that she storms out. Later, Sheldon comes in to see Leonard brought in a new couch and playing video games, which eventually causes Sheldon to find his later spot on the couch. When Leonard returns to make some rocket fuel for Howard, Sheldon points out that he made a mistake in the fuel formulation, and the botched rocket fuel prematurely activates. Leonard thinks he has plenty of time, but Sheldon saves his life by deducing that it is likely to explode quickly, and resolves the situation by sending it down the otherwise empty elevator. Leonard explains that the reason he puts up with Sheldon is that he saved his life and did not notify the authorities. When Penny questions Leonard's responsibility for the experiment that resulted in the destroyed elevator, he asks her what she was doing at the time, and she responds that she was studying, behaving well and doing charity work, when in reality she was jubilantly celebrating with her boyfriend after her pregnancy test came back negative. Leonard then returns to the apartment and apologizes to Sheldon, but the two then immediately get into another argument when Leonard starts watching Babylon 5, which Sheldon hates.

The guys set up an experiment on the building's roof to bounce a laser off the moon and back to Earth using the laser reflector left by the crew of Apollo 11. On Leonard's request, Penny arrives with her new boyfriend Zack. During the experiment, Zack turns out to be extremely ignorant and dimwitted, prompting Penny to break up with him. Later that night, Penny enters the guys' apartment drunk and has sex with Leonard. The next morning, Penny realizes what she had done and leaves the apartment embarrassed. Leonard, now thinking it is routine for friends to have "meaningless" casual sex, asks Leslie and then Penny to have sex with him, and both slam the door in his face. Meanwhile, Raj and Howard find a dating website and submit Sheldon's profile to the website without his knowledge to help him find a girlfriend. To their surprise, the dating site matches Sheldon with a woman named Amy Farrah Fowler. Sheldon initially refuses to meet Amy as he considers dating sites "hokum", but agrees when Raj and Howard blackmail him by claiming that they hid a dirty sock in the apartment. Amy bonds with Sheldon, having had an aversion to soiled hosiery and physical contact including coitus, sharing Sheldon's disbelief of dating websites and religion, and both their mothers' having similar personalities. Howard and Raj, shocked, regret what they have done.