The Desperation Emanation: Leonard realises he's the only one of the gang with no girlfriend. Sheldon wants to get rid of his when she hatches a plan for him to meet her mother. (S4 Ep5) [AD,S]
The Irish Pub Formulation: A visit from Raj's sister Priya creates tension among the guys, especially when Leonard asks Sheldon to conceal his romantic past with her. (S4 Ep6) [AD,S]
The Adhesive Duck Deficiency: Leonard, Raj and Howard go on a camping trip that alters their minds. Penny dislocates her shoulder when she slips in the shower. (S3 Ep8) [AD,S]
The Cornhusker Vortex: Sheldon teaches Leonard about American football so that he can try to fit in with Penny's friends. And Raj and Sheldon have a kite-fighting contest. (S3 Ep6) [AD,S]
The Guitarist Amplification: Sheldon is annoyed when Leonard and Penny argue about Penny's male friend staying over and he has to act as peacemaker. (S3 Ep7) [AD,S]
The Adhesive Duck Deficiency: Leonard, Raj and Howard go on a camping trip that alters their minds. Penny dislocates her shoulder when she slips in the shower. (S3 Ep8) [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 Boyfriend Complexity: When Penny's father visits, Leonard discovers that her parents still think that he and Penny are a couple, so he takes advantage of the situation. (S4 Ep9) [AD,S]
The Boyfriend Complexity: When Penny's father visits, Leonard discovers that her parents still think that he and Penny are a couple, so he takes advantage of the situation. (S4 Ep9) [AD,S]
The Alien Parasite Hypothesis: Amy realises that she has romantic feelings for Zack. Raj and Howard compete to prove who would make the better superhero. (S4 Ep10) [AD,S]
The Justice League Recombination: The guys slowly warm to Zack and find an enjoyable way to bond with him when they enter a New Year's Eve fancy dress competition together. (S4 Ep11) [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 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 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 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 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 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 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 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 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 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 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 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 Stag Convergence: Leonard, Sheldon and Raj throw a bachelor party for Howard, during which some stories about his sexual history are accidentally revealed. (S5 Ep22) [AD,S]
The Justice League Recombination: The guys slowly warm to Zack and find an enjoyable way to bond with him when they enter a New Year's Eve fancy dress competition together. (S4 Ep11) [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 Launch Acceleration: When NASA inform Howard that his space mission has been rescheduled to an earlier date, he tries to use the wedding as an excuse not to go. (S5 Ep23) [AD,S]
The Countdown Reflection: Bernadette decides that she wants to get married to Howard before his NASA space mission, but can they get organised in time? (S5 Ep24) [AD,S]
The Higgs Boson Observation: Amy is jealous when Sheldon hires an attractive female assistant, and Howard's return from space is delayed by a week. (S6 Ep3) [AD,S]
The Re-entry Minimization: Howard is disappointed when he doesn't receive a hero's welcome on his return from space. Will he ever get the recognition he deserves? (S6 Ep4) [AD,S]
The Cruciferous Vegetable Amplification: Sheldon realises that he won't live long enough to download his consciousness into a robot body, so he tries to extend his lifespan. (S4 Ep2) [AD,S]
The Robotic Manipulation: Penny tags along to Sheldon's first date with a woman he's been texting for months. Howard finds a new use for a robotic arm. (S4 Ep1) [AD,S]
The Lunar Excitation: Raj registers Sheldon for online dating and finds the perfect match: the female version of Sheldon. Penny seduces Leonard while she's drunk. (S3 Ep23) [AD,S]
The Creepy Candy Coating Corollary: Due to a childhood snub, Sheldon is irked when Star Trek actor Wil Wheaton (guest starring as himself) takes part in the same contest as him. (S3 Ep5) [AD,S]
The Pirate Solution: Raj must find a job or he'll be sent back to India, so he accepts an offer of work from Sheldon. Leonard and Penny try to get some time for themselves. (S3 Ep4) [AD,S]
The Gothowitz Deviation: Sheldon tries to modify Penny's behaviour, and rewards her with chocolate when she does what he wants, while Howard and Raj go to a goth nightclub. (S3 Ep3) [AD,S]
The Hot Troll Deviation: An embarrassing secret of Howard's comes to light as he tries to win back Bernadette. Sheldon and Raj have trouble working together. (S4 Ep4) [AD,S,W]
The Zazzy Substitution: The guys are concerned when a heartbroken Sheldon starts bulk buying cats after he breaks up with Amy, so Leonard tries to get Sheldon's mother to visit. (S4 Ep3) [AD,S,W]
The Plimpton Stimulation: When Sheldon meets a famous physicist online, he invites her over to the apartment, where she spends her time flirting with Leonard. (S3 Ep21) [AD,S,W]
The Spaghetti Catalyst: Sheldon hides his friendship with Penny from Leonard, but it isn't long before his double life is exposed. Can he remain friends with both of them? (S3 Ep20) [AD,S,W]
The Wheaton Recurrence: Leonard tells Penny that he loves her. The gang go bowling and find that Sheldon's enemy, Wil Wheaton, is playing in the opposing team. (S3 Ep19) [AD,S,W]
The Pants Alternative: Sheldon is awarded a prestigious prize but is scared of collecting the award at a ceremony because he knows he'll have to make a speech. (S3 Ep18) [AD,S,W]
The Classified Materials Turbulence: Things look up for Leonard when Penny makes a surprising revelation on her second date with Stuart. Howard sees a flaw in his NASA project. (S2 Ep22) [AD,S,W]
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,W]
The Cruciferous Vegetable Amplification: Sheldon realises that he won't live long enough to download his consciousness into a robot body, so he tries to extend his lifespan. (S4 Ep2) [AD,S,W]
The Robotic Manipulation: Penny tags along to Sheldon's first date with a woman he's been texting for months. Howard finds a new use for a robotic arm. (S4 Ep1) [AD,S,W]
The Precious Fragmentation: The gang squabble over a ring that they believe was used in The Lord of the Rings movies, and Sheldon seems to be turning into Gollum. (S3 Ep17) [AD,S,W]
The Excelsior Acquisition: Sheldon is summoned to court for driving through a red light. He misses the chance to meet Stan Lee and riles the judge. Will he go to prison? (S3 Ep16) [AD,S,W]
The Large Hadron Collision: Sheldon is gutted when Leonard asks Penny to go to Switzerland on Valentine's Day to see the world's largest particle accelerator instead of him. (S3 Ep15) [AD,S,W]
The Einstein Approximation: Sheldon is baffled by a formula he's working on, so he gets a less mentally taxing job at the Cheesecake Factory to kick-start his creativity. (S3 Ep14) [AD,S,W]
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,W]
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,W]
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,W]
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,W]
The Lunar Excitation: Raj registers Sheldon for online dating and finds the perfect match: the female version of Sheldon. Penny seduces Leonard while she's drunk. (S3 Ep23) [AD,S]
The Bozeman Reaction: After Leonard and Sheldon's flat is burgled, the gang create a new state-of-the-art security system to outwit any thieves and protect the place. (S3 Ep13) [AD,S]
The Psychic Vortex: Sheldon and Raj go to a university party where Raj lusts after a girl called Abby. Leonard regrets telling Penny that he disapproves of her belief in psychics. (S3 Ep12) [AD,S]
The Maternal Congruence: Leonard is horrified when his mother turns up unannounced for a Christmas visit, and then he finds out that Sheldon knew about her divorce before him. (S3 Ep11) [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 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 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 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 21-Second Excitation: The gang's plans to attend a film screening are scuppered by Sheldon's nemesis Wil Wheaton. Penny and Bernadette invite Amy to her first slumber party. (S4 Ep8) [AD,S,W]
The Apology Insufficiency: Leonard thinks his dating problems are due to a lack of confidence, and vows to be self-assured around attractive women. Howard is called by the FBI. (S4 Ep7) [AD,S,W]
The Irish Pub Formulation: A visit from Raj's sister Priya creates tension among the guys, especially when Leonard asks Sheldon to conceal his romantic past with her. (S4 Ep6) [AD,S,W]
The Desperation Emanation: Leonard realises he's the only one of the gang with no girlfriend. Sheldon wants to get rid of his when she hatches a plan for him to meet her mother. (S4 Ep5) [AD,S,W]
The Hot Troll Deviation: An embarrassing secret of Howard's comes to light as he tries to win back Bernadette. Sheldon and Raj have trouble working together. (S4 Ep4) [AD,S,W]
The Zazzy Substitution: The guys are concerned when a heartbroken Sheldon starts bulk buying cats after he breaks up with Amy, so Leonard tries to get Sheldon's mother to visit. (S4 Ep3) [AD,S,W]
The Cruciferous Vegetable Amplification: Sheldon realises that he won't live long enough to download his consciousness into a robot body, so he tries to extend his lifespan. (S4 Ep2) [AD,S,W]
The Robotic Manipulation: Penny tags along to Sheldon's first date with a woman he's been texting for months. Howard finds a new use for a robotic arm. (S4 Ep1) [AD,S]
The Lunar Excitation: Raj registers Sheldon for online dating and finds the perfect match: the female version of Sheldon. Penny seduces Leonard while she's drunk. (S3 Ep23) [AD,S]
The Plimpton Stimulation: When Sheldon meets a famous physicist online, he invites her over to the apartment, where she spends her time flirting with Leonard. (S3 Ep21) [AD,S]
The Spaghetti Catalyst: Sheldon hides his friendship with Penny from Leonard, but it isn't long before his double life is exposed. Can he remain friends with both of them? (S3 Ep20) [AD,S]
The Adhesive Duck Deficiency: Leonard, Raj and Howard go on a camping trip that alters their minds. Penny dislocates her shoulder when she slips in the shower. (S3 Ep8) [AD,S]
The Guitarist Amplification: Sheldon is annoyed when Leonard and Penny argue about Penny's male friend staying over and he has to act as peacemaker. (S3 Ep7) [AD,S]