Penny tags along on Sheldon's first date; Wolowitz finds a new use for a robotic arm.
Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.
When Sheldon searches for an alternative to human companionship, the guys become concerned.
An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.
Leonard realizes he is the only one in his group without a girlfriend; Sheldon wants to get rid of his girlfriend.
Leonard keeps an affair a secret from Sheldon, Howard and Raj.
Sheldon's interview with the FBI jeopardizes Wolowitz's security clearance.
While the guys camp out for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.
Penny asks Leonard to lie to her father (Keith Carradine); Howard, Raj and Bernadette pull an all-nighter at a telescope.
Amy realizes she has feelings for Penny's ex; Koothrappali and Wolowitz try to prove who would be a better superhero.
The guys try to bond with Penny's new boyfriend through a costume contest.
Leonard's idea for a smartphone application causes friction in his friendship with Sheldon.
Bernadette runs into her ex-boyfriend (Rick Fox) while attending a science event with Wolowitz.
Sheldon takes acting lessons from Penny in hope of becoming a better teacher; Koothrappali fantasizes about his friend's girlfriend.
A wealthy donor makes Leonard question what he is willing to do for science.
Wolowitz considers taking things with Bernadette to the next level; Leonard and Raj's sister rekindle their relationship.
Sheldon is upset when he realizes Leonard is the center of their group of friends.
Leonard has to choose between Penny and his new girlfriend, Priya; Howard's magic trick drives Sheldon crazy.
The guys try to figure out who hacked Sheldon's online-game account.
Amy and Sheldon spread gossip as part of an experiment; Howard decides to take a big step in his relationship with Bernadette.
Priya dissects the roommate agreement; the ladies take Sheldon dancing.
Raj tries to cure his social anxiety; Penny spies on Leonard and his girlfriend through Bernadette.
Howard's mom winds up in the hospital after hearing news of her son's engagement to Bernadette.