Penny finds herself along for the ride on Sheldon's first date ever; while Wolowitz finds a new use for a robotic arm.
Sheldon realizes he won't live long enough to download his consciousness into a robot body, and attempts to extend his lifespan.
The guys are concerned as Sheldon searches for an alternative to human companionship.
An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work.
Leonard realizes he's the only one without a girlfriend, while Sheldon wants to get rid of his.
Leonard keeps an affair secret from Sheldon, Howard and Raj.
Sheldon's answers during an FBI interview put Wolowitz's security clearance in jeopardy.
While the guys camp in line for a screening, Penny and Bernadette invite Amy to her first slumber party.
Penny asks Leonard to lie to her father, while Howard, Raj and Bernadette pull an all-nighter at a telescope.
Amy finds she has sexual feelings for Penny's ex, while Koothrappali and Wolowitz try to prove who would be the better superhero.
The guys find a "super" use for Penny's new boyfriend, Zack, when they enter a costume contest as the Justice League.
Leonard's idea for a smartphone app derails his friendship with Sheldon.
Tension runs high when everyone is staying at the same hotel for a science event and Bernadette runs into her ex-boyfriend.
Sheldon hopes acting lessons from Penny will help him become a better teacher. Meanwhile, Koothrappali fantasizes about his best friend's girlfriend.
Wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science.
As Wolowitz contemplates taking things with Bernadette to the next level, Leonard rekindles his relationship with Raj's sister.
Sheldon struggles to cope when he realizes it's actually Leonard who is the center of their social group.
Leonard must choose between new girlfriend Priya and his friendship with Penny. Meanwhile, Howard drives Sheldon crazy with a magic trick.
When someone hacks Sheldon's online game account, the guys go on a quest to find the culprit.
Sheldon and Amy experiment on their friends by spreading gossip, while Howard takes a big step in his relationship with Bernadette.
When Priya uses her lawyer skills to pick apart the roommate agreement, the girls take Sheldon dancing.
Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.
When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.
When Bernadette receives her Ph.D., the guys take joy in reminding an emasculated Wolowitz that he is the only one in their group who isn't a doctor. Meanwhile, Koothrappali becomes Sheldon's new roommate after hearing Leonard and Priya engaging in a "Star Trek" bedroom fantasy.