Thursdays 8:00 PM on CBS
The-big-bang-theory
"The Peanut Reaction"

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 Porkchop Indeterminacy"

The guys meet Sheldon's extremely attractive twin sister Missy (Courtney Henggeler) who is in town for a wedding.

"The Nerdvana Annihilation"

Leonard buys a replica time machine online from the 1960 film The Time Machine and ends up splitting it with the guys.

"The Bat Jar Conjecture"

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.

"The Jerusalem Duality"

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."

"The Pancake Batter Anomaly"

Penny returns from a visiting family in Nebraska with a cold causing Sheldon to freak out because he's a bit of a germaphone.

"The Loobenfeld Decay"

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.

"The Cooper-Hofstadter Polarization"

After cleaning up after an internet experiment, Leonard discovers a letter in the trash can inviting the roommates to present some research they've done to a physics conference.

"The Grasshopper Experiment"

Raj is scared when his parents arrange a blind date for him with a girl from his childhood as he's still unable to women. Penny takes up bar tending to make some extra money.

"The Dumpling Paradox"

Penny's slutty friend, Chrissy (Brooke D'Orsay) from Nebraska, is in town and is seduced by Wolowitz. The pair ends up taking over Penny's apartment, forcing her to sleep on Leonard and Sheldon's couch.