The Shiksa Indeterminacy: Leonard, Raj and Howard all fall heavily for Sheldon's twin sister, but when Leonard comes up with a plan to win her heart, it's derailed by Sheldon. (S1 Ep15) [AD,S]
The Peanut Reaction: Penny throws a surprise party for Leonard, with help from Howard and Raj, but Sheldon's indulgence in an electronics shop throws her off track. (S1 Ep16) [AD,S]
The Comic-Con Conundrum: Cut off from his father's fortune, Raj appoints Sheldon to organise his finances. Penny considers joining the guys at Comic-Con. (S10 Ep17) [AD,S]
The Escape Hatch Identification: Leonard and Penny offer Sheldon's old room to Raj when he's forced to move out of his flat, leading to unexpected conflict. (S10 Ep18) [AD,S]
The Thespian Catalyst: Sheldon lectures at the university but worries that the students don't seem to like him. Raj fantasises about his best friend's girlfriend. (S4 Ep14) [AD,S]
The Benefactor Factor: A wealthy benefactor at the university makes Leonard consider how far he's willing to go in the name of science. (S4 Ep15) [AD,S]
The Cohabitation Formulation: Howard is torn between taking things to the next level with Bernadette and pleasing his mother. Leonard rekindles his relationship with Priya. (S4 Ep16) [AD,S]
The Toast Derivation: Sheldon is surprised and disturbed to find out that it's really Leonard who is at the centre of their group of friends and not him. (S4 Ep17) [AD,S]
The Flaming Spittoon Acquisition: Stuart from the comic book shop invites Amy out on a date. Consumed by jealousy, Sheldon then asks her to be his girlfriend. (S5 Ep10) [AD,S]
The Speckerman Recurrence: Leonard confronts the man who bullied him in high school, while Penny realises that she did her fair share of tormenting in the past. (S5 Ep11) [AD,S]
The Shiny Trinket Maneuver: When Sheldon is dismissive of Amy's career, Penny, Raj and Leonard teach him that sometimes it's a good idea to pretend to care about things. (S5 Ep12) [AD,S]
The Recombination Hypothesis: In the 100th episode of the US sitcom, Leonard and Penny agree to give their relationship another chance, but they soon start to argue again. (S5 Ep13) [AD,S]
The Vartabedian Conundrum: Leonard goes to Penny for help when his relationship with Stephanie takes off faster than he'd like, but will he act on her advice? (S2 Ep10) [AD,S]
The Bath Item Gift Hypothesis: At Christmas, Leonard's hunky colleague starts dating Penny, while Sheldon's obsession with gift-giving etiquette torments everyone. (S2 Ep11) [AD,S]
The Killer Robot Instability: Kripke challenges the boys to a robot duel, while Howard is devastated when Penny finally tells him what she thinks of his chauvinism. (S2 Ep12) [AD,S]
The Friendship Algorithm: Sheldon develops a scientific procedure for making friends when he discovers that Kripke has control of a new supercomputer at the university. (S2 Ep13) [AD,S]
The Thanksgiving Decoupling: Howard takes the gang to his mother's house for Thanksgiving to protect himself from his grumpy father-in-law who has also been invited. (S7 Ep9) [AD,S]
The Discovery Dissipation: Sheldon feels guilty when he gets attention for his accidental discovery of a new element. Raj stays with Howard and Bernadette for a week. (S7 Ep10) [AD,S]
The Thanksgiving Decoupling: Howard takes the gang to his mother's house for Thanksgiving to protect himself from his grumpy father-in-law who has also been invited. (S7 Ep9) [AD,S]
The Discovery Dissipation: Sheldon feels guilty when he gets attention for his accidental discovery of a new element. Raj stays with Howard and Bernadette for a week. (S7 Ep10) [AD,S]
The Thanksgiving Decoupling: Howard takes the gang to his mother's house for Thanksgiving to protect himself from his grumpy father-in-law who has also been invited. (S7 Ep9) [AD,S]
The Thanksgiving Decoupling: Howard takes the gang to his mother's house for Thanksgiving to protect himself from his grumpy father-in-law who has also been invited. (S7 Ep9) [AD,S]
The Tangerine Factor: When Penny breaks up with her boyfriend, Leonard plucks up the courage to ask her out. And each of them turns to Sheldon for advice about their date. (S1 Ep17) [AD,S]
The Bad Fish Paradigm: Penny opens up to a reluctant Sheldon after a less-than-stellar first date with Leonard, putting him in the awkward position of having to keep a secret. (S2 Ep1) [AD,S]
The Collaboration Fluctuation: Leonard, Penny and Raj settle into their new living arrangement, and Sheldon expresses an interest in Amy's professional life. (S10 Ep19) [AD,S]
The Recollection Dissipation: Sheldon collaborates on two projects - one with Leonard and Howard, plus another with Amy - pushing himself to the limit. (S10 Ep20) [AD,S]
The Collaboration Fluctuation: Leonard, Penny and Raj settle into their new living arrangement, and Sheldon expresses an interest in Amy's professional life. (S10 Ep19) [AD,S]
The Recollection Dissipation: Sheldon collaborates on two projects - one with Leonard and Howard, plus another with Amy - pushing himself to the limit. (S10 Ep20) [AD,S]
The Prestidigitation Approximation: Leonard must choose between his new girlfriend Priya and his friendship with Penny. Howard drives Sheldon crazy with a magic trick. (S4 Ep18) [AD,S]
The Zarnecki Incursion: When somebody hacks into Sheldon's online gaming account, he and his friends become determined to locate the culprit. (S4 Ep19) [AD,S]
The Herb Garden Germination: Sheldon and Amy experiment on their friends by spreading gossip, while Howard takes a big step in his relationship with Bernadette. (S4 Ep20) [AD,S]
The Prestidigitation Approximation: Leonard must choose between his new girlfriend Priya and his friendship with Penny. Howard drives Sheldon crazy with a magic trick. (S4 Ep18) [AD,S]
The Agreement Dissection: Priya uses her legal expertise to dissect the roommate agreement and put Sheldon in his place, and the girls take Sheldon dancing. (S4 Ep21) [AD,S]
The Zarnecki Incursion: When somebody hacks into Sheldon's online gaming account, he and his friends become determined to locate the culprit. (S4 Ep19) [AD,S]
The Herb Garden Germination: Sheldon and Amy experiment on their friends by spreading gossip, while Howard takes a big step in his relationship with Bernadette. (S4 Ep20) [AD,S]
The Agreement Dissection: Priya uses her legal expertise to dissect the roommate agreement and put Sheldon in his place, and the girls take Sheldon dancing. (S4 Ep21) [AD,S]
The Beta Test Initiation: Leonard and Penny put their relationship through a 'beta test' and report problems with each other as 'bugs'. Sheldon and Amy seek internet fame. (S5 Ep14) [AD,S]
The Friendship Contraction: After Sheldon keeps him awake all night, an irate Leonard decides he needs to break the roommate agreement, which formally ends their friendship. (S5 Ep15) [AD,S]
The Vacation Solution: Sheldon helps Amy in her biology lab after he is forced to use up two weeks of holiday, but he is bored by the tasks that she gives him. (S5 Ep16) [AD,S]
The Beta Test Initiation: Leonard and Penny put their relationship through a 'beta test' and report problems with each other as 'bugs'. Sheldon and Amy seek internet fame. (S5 Ep14) [AD,S]
The Rothman Disintegration: Sheldon and Kripke argue over who should get Professor Rothman's vacant corner office. Amy buys Penny some art to celebrate their friendship. (S5 Ep17) [AD,S]
The Friendship Contraction: After Sheldon keeps him awake all night, an irate Leonard decides he needs to break the roommate agreement, which formally ends their friendship. (S5 Ep15) [AD,S]
The Vacation Solution: Sheldon helps Amy in her biology lab after he is forced to use up two weeks of holiday, but he is bored by the tasks that she gives him. (S5 Ep16) [AD,S]
The Rothman Disintegration: Sheldon and Kripke argue over who should get Professor Rothman's vacant corner office. Amy buys Penny some art to celebrate their friendship. (S5 Ep17) [AD,S]
The Financial Permeability: When Sheldon lends Penny some money, it brings her ex-boyfriend Kurt back into her life, with negative consequences for the gang. (S2 Ep14) [AD,S]
The Maternal Capacitance: A disastrous visit from Leonard's mother has the unexpected side-effect of bringing Leonard and Penny closer together. (S2 Ep15) [AD,S]
The Cushion Saturation: A game of paintball leads to a squabble when Penny accidentally shoots paint at one of Sheldon's cushions. Romance blossoms between Howard and Leslie. (S2 Ep16) [AD,S]
The Terminator Decoupling: Leonard, Sheldon, Howard and Raj discover that beautiful sci-fi actress Summer Glau is on board their train to San Francisco. (S2 Ep17) [AD,S]
The Cooper Extraction: Sheldon has to go back to Texas when his sister goes into labour. While he's away, the gang gather at the flat to decorate the Christmas tree. (S7 Ep11) [AD,S]
The Hesitation Ramification: Penny's big TV acting break hits the cutting-room floor, so Leonard does his best to comfort her, which leads her to ask him a bold question. (S7 Ep12) [AD,S]
The Cooper Extraction: Sheldon has to go back to Texas when his sister goes into labour. While he's away, the gang gather at the flat to decorate the Christmas tree. (S7 Ep11) [AD,S]
The Hesitation Ramification: Penny's big TV acting break hits the cutting-room floor, so Leonard does his best to comfort her, which leads her to ask him a bold question. (S7 Ep12) [AD,S]
The Cooper Extraction: Sheldon has to go back to Texas when his sister goes into labour. While he's away, the gang gather at the flat to decorate the Christmas tree. (S7 Ep11) [AD,S]
The Cooper Extraction: Sheldon has to go back to Texas when his sister goes into labour. While he's away, the gang gather at the flat to decorate the Christmas tree. (S7 Ep11) [AD,S]
The Codpiece Topology: Seeing Penny out on a date with another guy sends a distressed Leonard rushing back to Leslie Winkle, much to Sheldon's dismay. (S2 Ep2) [AD,S]
The Barbarian Sublimation: Penny becomes addicted to an online game based on the world of Conan the Barbarian and begins to pester Sheldon for advice. (S2 Ep3) [AD,S]
The Separation Agitation: Howard and Bernadette are upset when they leave Halley at the nursery. Bert the geologist introduces his girlfriend to the gang. (S10 Ep21/24) [AD,S]
The Cognition Regeneration: Leonard isn't happy when he finds out that Penny is considering accepting a job offer from her ex-boyfriend Zack. (S10 Ep22/24) [AD,S]
The Separation Agitation: Howard and Bernadette are upset when they leave Halley at the nursery. Bert the geologist introduces his girlfriend to the gang. (S10 Ep21/24) [AD,S]
The Cognition Regeneration: Leonard isn't happy when he finds out that Penny is considering accepting a job offer from her ex-boyfriend Zack. (S10 Ep22/24) [AD,S]
The Wildebeest Implementation: Raj attempts to overcome his anxiety about talking to women, while Penny uses Bernadette to spy on Leonard and his girlfriend. (S4 Ep22) [AD,S]
The Engagement Reaction: Howard finally tells his mother that he's engaged to Bernadette. Unfortunately, the news lands his mum in hospital. (S4 Ep23) [AD,S]
The Roommate Transmogrification: Raj decides to move in with Sheldon after hearing Leonard and Priya engaging in a Star Trek bedroom fantasy. (S4 Ep24) [AD,S]
The Wildebeest Implementation: Raj attempts to overcome his anxiety about talking to women, while Penny uses Bernadette to spy on Leonard and his girlfriend. (S4 Ep22) [AD,S]
The Skank Reflex Analysis: Penny worries that she's screwed things up with her friends after her night with Raj. Sheldon takes command of the paintball team. (S5 Ep1) [AD,S]
The Engagement Reaction: Howard finally tells his mother that he's engaged to Bernadette. Unfortunately, the news lands his mum in hospital. (S4 Ep23) [AD,S]
The Roommate Transmogrification: Raj decides to move in with Sheldon after hearing Leonard and Priya engaging in a Star Trek bedroom fantasy. (S4 Ep24) [AD,S]
The Skank Reflex Analysis: Penny worries that she's screwed things up with her friends after her night with Raj. Sheldon takes command of the paintball team. (S5 Ep1) [AD,S]
The Werewolf Transformation: Sheldon's well-organised world is turned upside down when he learns that the barber who has cut his hair for years is ill in hospital. (S5 Ep18) [AD,S]
The Weekend Vortex: Amy is upset when Sheldon breaks his promise to attend her aunt's birthday party in order to join the guys for a Star Wars video game marathon instead. (S5 Ep19) [AD,S]
The Transporter Malfunction: Penny buys Leonard and Sheldon some Star Trek memorabilia, but she is irked when they refuse to remove the toys from their packaging. (S5 Ep20) [AD,S]
The Werewolf Transformation: Sheldon's well-organised world is turned upside down when he learns that the barber who has cut his hair for years is ill in hospital. (S5 Ep18) [AD,S]
The Hawking Excitation: When Stephen Hawking comes to lecture at the university, Howard is given the task of maintaining his wheelchair, which makes Sheldon envious. (S5 Ep21) [AD,S]
The Weekend Vortex: Amy is upset when Sheldon breaks his promise to attend her aunt's birthday party in order to join the guys for a Star Wars video game marathon instead. (S5 Ep19) [AD,S]
The Transporter Malfunction: Penny buys Leonard and Sheldon some Star Trek memorabilia, but she is irked when they refuse to remove the toys from their packaging. (S5 Ep20) [AD,S]
The Hawking Excitation: When Stephen Hawking comes to lecture at the university, Howard is given the task of maintaining his wheelchair, which makes Sheldon envious. (S5 Ep21) [AD,S]
The Work Song Nanocluster: Penny's home-based business selling hair accessories gets out of hand when an overexcited Sheldon takes charge of production. (S2 Ep18) [AD,S]
The Dead Hooker Juxtaposition: Penny develops a rivalry with a sexy female neighbour who moves into the apartment building and threatens to become the 'new Penny'. (S2 Ep19) [AD,S]
The Hofstadter Isotope: Leonard is devastated when Stuart from the comic book shop chats up Penny. Even worse, she doesn't mind. Sheldon tries to scupper the budding romance. (S2 Ep20) [AD,S]
The Vegas Renormalization: Leonard and Raj take a heartbroken Howard to Las Vegas, leaving Sheldon locked out of his flat and forced to stay with Penny. (S2 Ep21) [AD,S]
The Nerdvana Annihilation: When Penny makes fun of Leonard's habit of collecting goofy memorabilia, his friends kick up a fuss and try to keep him on the side of the nerds. (S1 Ep14) [AD,S]
The Bat Jar Conjecture: Sheldon is ousted from the gang's Physics Bowl quiz team, so he decides to prove his superiority by forming his own team for the event. (S1 Ep13) [AD,S]
The Pancake Batter Anomaly: Penny volunteers to nurse Sheldon when he's sick. But his friends, who know how miserable he is when he's ill, stay well away. (S1 Ep11) [AD,S]
The Maternal Conclusion: Leonard is surprised when his mother Beverly comes to visit and is kind to him, until he finds out the real reason she's there. (S12 Ep22) [AD,S]
The Plagiarism Schism: Barry Kripke finds proof that Dr Pemberton plagiarised his thesis in college. Should Sheldon and Amy turn in their rival? (S12 Ep21) [AD,S]
The Loobenfeld Decay: Leonard and Sheldon each tell a lie to avoid going to see Penny singing on stage in a production of Rent, but Sheldon's fib gets out of control. (S1 Ep10) [AD,S]
The Cooper-Hofstadter Polarization: Sheldon and Leonard fall out when they're asked to collaborate at a physics conference. Penny tries to help but just makes things worse. (S1 Ep9) [AD,S]
The Grasshopper Experiment: Raj panics when his parents arrange a blind date for him. But he discovers that he can talk to her - after a few drinks. (S1 Ep8) [AD,S]
The Dumpling Paradox: When Howard seduces Penny's friend and spends the night with her in Penny's flat, Penny asks if she can sleep on Leonard and Sheldon's sofa. (S1 Ep7) [AD,S]
The Decision Reverberation: Raj publishes a paper that suggests he may have discovered alien life. Penny encourages Leonard to stand up for himself. (S12 Ep20) [AD,S]
The Inspiration Deprivation: Amy has a meltdown when she feels the pressure of what it would mean for women everywhere if she were to win a Nobel Prize. (S12 Ep19) [AD,S]
The Middle Earth Paradigm: Penny's Halloween party puts Leonard, Sheldon, Howard and Raj through a demanding new test of their social skills. (S1 Ep6) [AD,S]
The Hamburger Postulate: Leonard thinks he's been wasting his time on Penny, so he turns his attention to Leslie. Sheldon's uncomfortable with a change to his hamburger routine. (S1 Ep5) [AD,S]
The Luminous Fish Effect: Getting fired forces Sheldon to ponder life outside physics, so Leonard has to take drastic action to snap his friend out of his reverie. (S1 Ep4) [AD,S]
The Fuzzyboots Corollary: Leonard is upset when he discovers that Penny is seeing someone, so he plucks up the courage to ask a woman out on a date. (S1 Ep3) [AD,S]
The Laureate Accumulation: When their academic competitors charm America on a publicity tour, Sheldon and Amy try to get some Nobel laureates on their side. (S12 Ep18) [AD,S]
The Conference Valuation: Penny and Bernadette go to San Diego for a sales convention, leaving Howard in charge of Michael and Halley while they're away. (S12 Ep17) [AD,S]
The D & D Vortex: When the gang find out that Wil Wheaton is hosting a celebrity game of Dungeons & Dragons at his home, deception and betrayal take hold. (S12 Ep16) [AD,S]
The Donation Oscillation: Penny attempts to sabotage Leonard's efforts to help her ex-boyfriend Zack and his wife Marissa have a family of their own. (S12 Ep15) [AD,S]
The Meteorite Manifestation: Sheldon is thrilled to help Howard and Bernadette with some bureaucratic paperwork, until he realises that they're breaking the law. (S12 Ep14) [AD,S]
The Confirmation Polarization: Sheldon and Amy are thrilled when their super-asymmetry theory is proved correct. Bernadette enjoys some big success at work. (S12 Ep13) [AD,S]
The Propagation Proposition: Penny's ex-boyfriend Zack and his wife want a baby, but when they encounter fertility problems, they ask Leonard for his help. (S12 Ep12) [AD,S]
The Paintball Scattering: Jealousy, trust issues and tension among the couples in the gang cause mayhem when Penny and Leonard organise a paintball game. (S12 Ep11) [AD,S]
The VCR Illumination: Sheldon and Amy are still upset about their theory being disproven, but a video tape from Sheldon's past inspires him not to give up. (S12 Ep10) [AD,S]
The Citation Negation: Sheldon and Amy get some devastating news. Bernadette asks Stuart's girlfriend Denise to teach her how to beat Howard at a video game. (S12 Ep9) [AD,S]
The Consummation Deviation: Sheldon aims to bond with Amy's father, but Howard lures Mr Fowler away with his magic tricks. Raj and Anu try to get physical. (S12 Ep8) [AD,S]
The Grant Allocation Derivation: Leonard is made responsible for distributing extra grant money. Bernadette turns the garden playhouse into a hideaway to escape her family. (S12 Ep7) [AD,S]
The Romance Recalibration: Penny thinks that Leonard has stopped making an effort in their relationship, so she decides to go away for a spa weekend with Amy. (S10 Ep13) [AD,S]
The Bitcoin Entanglement: Sheldon seeks revenge when the guys cut him out of a potentially valuable investment. A secret about Leonard and Penny is revealed. (S11 Ep9) [AD,S]
The Tesla Recoil: Leonard and Howard learn that Sheldon went to work with the military behind their backs. Bernadette thinks Ruchi's trying to steal her job. (S11 Ep8) [AD,S]
The Geology Methodology: Sheldon and Bert collaborate on a research project, but Sheldon feels embarrassed to be associated with the study of geology. (S11 Ep7) [AD,S]
The Retraction Reaction: Leonard angers the university during an embarrassing interview. Amy and Bernadette must hide their success from Sheldon and Howard. (S11 Ep2) [AD,S]
The Proposal Proposal: Amy must decide whether or not to marry Sheldon and gives him an answer to his proposal. Howard and Bernadette struggle with some unexpected news. (S11 Ep1) [AD,S]
The Recollection Dissipation: Sheldon collaborates on two projects - one with Leonard and Howard, plus another with Amy - pushing himself to the limit. (S10 Ep20) [AD,S]
The Collaboration Fluctuation: Leonard, Penny and Raj settle into their new living arrangement, and Sheldon expresses an interest in Amy's professional life. (S10 Ep19) [AD,S]
The Escape Hatch Identification: Leonard and Penny offer Sheldon's old room to Raj when he's forced to move out of his flat, leading to unexpected conflict. (S10 Ep18) [AD,S]
The Locomotion Reverberation: Leonard and Howard distract Sheldon with a trip to a historic railway when he slows their progress on the guidance system. (S10 Ep15) [AD,S]
The Emotion Detection Automation: Sheldon tests a new invention after hearing that it could help him to read people's emotions. Raj seeks dating advice. (S10 Ep14) [AD,S]
The Romance Recalibration: Penny thinks that Leonard has stopped making an effort in their relationship, so she decides to go away for a spa weekend with Amy. (S10 Ep13) [AD,S]
The Holiday Summation: After spending Christmas apart, the gang gather at Penny and Leonard's flat and hear about Sheldon and Amy's terrible trip to Texas. (S10 Ep12) [AD,S]
The Birthday Synchronicity: Sheldon and Amy try to celebrate her birthday with an intimate night at home but are interrupted when Bernadette goes into labour. (S10 Ep11) [AD,S]
The Geology Elevation: Sheldon can't contain his jealousy when he hears that his university colleague, Bert the geologist, has won a prestigious fellowship. (S10 Ep9) [AD,S]
The Brain Bowl Incubation: Sheldon tries to convince Amy that they should procreate. Raj feels embarrassed about what the new woman in his life does for a living. (S10 Ep8) [AD,S]
The Veracity Elasticity: Leonard is upset when he finds out that Penny has been moving his collectables out of Sheldon's old room and into storage behind his back. (S10 Ep7) [AD,S]
The Fetal Kick Catalyst: Penny meets her fans at a comic book convention. Sheldon and Amy host brunch at Penny's flat. Howard makes an impulsive purchase. (S10 Ep6) [AD,S]
The Hot Tub Contamination: Leonard and Penny intervene when Sheldon and Amy have an argument. Howard and Bernadette are disturbed by unexpected guests. (S10 Ep5) [AD,S]
The Cohabitation Experimentation: When Amy's flat is flooded, she has to move out while it is being repaired and proposes a 'cohabitation experiment' with Sheldon. (S10 Ep4) [AD,S]