Mensa-fied best friends and roommates Leonard and Sheldon, physicists who work at the California Institute of Technology, may be able to tell everybody more than they want to know about quantum physics, but getting through most basic social situations, especially ones involving women, totally baffles them. How lucky, then, that babe-alicious waitress/aspiring actress Penny moves in next door. Frequently seen hanging out with Leonard and Sheldon are friends and fellow Caltech scientists Wolowitz and Koothrappali. Will worlds collide? Does Einstein theorize in the woods?
Howard uses a robotic arm for his own pleasure. Sheldon goes on a date with Amy Farrah Fowler, and Penny finds herself accompanying them. S4, Ep1
Cruciferous Veg Amplification. Sheldon calculates that he'll be dead before technology exists to download his consciousness into a robot, so he goes on a healthy-living binge. S4, Ep2
Sheldon breaks up with Amy Farrah Fowler, and the guys worry when he starts replacing her with cats. S4, Ep3
Wolowitz is embarrassed when a secret of his is revealed, and Sheldon and Raj battle at work. S4, Ep4
Sheldon meets Amy's mum and comes to the realisation he no longer wants to see Amy, and Leonard realises everyone is in a relationship except for him. S4, Ep5
When Raj's sister has a one-day layover, he forbids the others from hooking up with her, unaware she and Leonard already did long ago. S4, Ep6
The rest of the gang is interviewed by the FBI for Wolowitz's security clearance, with Sheldon accidentally letting slip some damaging information. S4, Ep7
The guys camp out to see a print of Raiders of the Lost Ark with 21 extra seconds and are outraged to see Wil Wheaton and his friends skip the line. S4, Ep8
Penny asks Leonard to lie to her visiting father, while Howard, Raj and Bernadette spend all night looking through a telescope. S4, Ep9
Amy crushes on one of Penny's dim ex-boyfriends, Zack. Raj and Wolowitz argue over who'd be the better superhero. S4, Ep10
Justice League Recombination. The guys get Zack and Penny to join their Justice League costume for a New Year's Eve bash at the comic book store. S4, Ep11
Their friendship becomes strained when Sheldon tries to take over Leonard's creation of a smartphone application that solves differential equations. S4, Ep12
Howard is jealous when Bernadette runs into her old boyfriend at a science event they're attending. S4, Ep13
Sheldon wants acting lessons from Penny, hoping they will make him a better teacher. S4, Ep14
After meeting at a fundraising gala, an aged but wealthy Caltech donor makes Leonard ponder if he's willing to have sex with her to secure a donation. S4, Ep15
Howard contemplates a serious decision in his relationship with Bernadette, and Leonard and Raj's sister start seeing each other again. S4, Ep16
Sheldon is in a crisis when he realises he's not the epicentre of the group, so he decides to find new friends. S4, Ep17
Leonard has a tough choice to make when Priya asks him to stop spending time with Penny, and Howard keeps pestering Sheldon with a magic trick. S4, Ep18
The guys become sleuths to find out who hacked Sheldon's online-game account. S4, Ep19
Sheldon and Amy decide to start rumours about themselves as a social test. Howard takes his relationship with Bernadette to an even higher level. S4, Ep20
Priya uses her legal expertise to rip apart Sheldon's roommate agreement, and the women take the flustered Sheldon out dancing. S4, Ep21
Raj makes an attempt to cure his phobia of talking to women, and Penny spies on Leonard and Priya with the help of Bernadette. S4, Ep22
Mrs. Wolowitz ends up in the hospital after Howard tells her he's marrying Bernadette. While there, Leonard stresses over Penny and Priya. S4, Ep23
Mrs. Wolowitz ends up in the hospital after Howard tells her he's marrying Bernadette. While there, Leonard stresses over Penny and Priya. S4, Ep24