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The guys return from the Renaissance fair and see Penny has already moved on to a new guy, Eric (Travis Schuldt), prompting Leonard to pursue a relationship with prior fling Leslie Winkle.
Penny and Leonard return from their date from the end of season one and Leonard finds Howard and Raj spying on them via webcam.
Penny breaks up with her boyfriend after he posted intimate details about her on his blog. Leonard tries to comfort her but accidentally sends her back into the arms of her boyfriend.
When the boys go to eat at Penny's restaurant, she learns Leonard has never had a birthday before. She decides to throw him a surprise party and blackmails Leonard into helping.
The guys meet Sheldon's extremely attractive twin sister Missy (Courtney Henggeler) who is in town for a wedding.
Leonard buys a replica time machine online from the 1960 film The Time Machine and ends up splitting it with the guys.
The guys compete in a physics bowl after the previous contestants dropped out to form a barbershop quartet. When Sheldon's showboating becomes too much for them, they kick him off the team.
Sheldon becomes insecure over his intelligence because of a smarter 15-year-old prodigy Dennis Kim. He decides his work is useless and he aims for the Nobel Peace Prize by creating a "Nuevo Jerusalem."
Penny returns from a visiting family in Nebraska with a cold causing Sheldon to freak out because he's a bit of a germaphone.
When Penny is given a part in Rent, the boys try to avoid to see her show after hearing her sing "Out Tonight" out of key in order to not hurt her feelings.