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'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.
The guys are invited to Penny's Halloween party and decide to go only when the idea of costumes are mentioned. At the party, Wolowitz and Leonard attempt to socialize until Penny's ex, Kurt, shows up and humiliates Leonard.
While eating at the Cheesecake Factory where Penny works, the guys run into Leslie Winkle, the girl who previously rejected Leonard. Leslie asks Leonard to play in her string quartet as the cellist, but what she really wants is him.
Sheldon is fired from his job at Caltech when he insults his boss Dr. Eric Gablehauser. Unemployed, Sheldon quickly spirals into depressions which Leonard tries to end by bringing over Sheldon's mother.
When Leonard witnesses Penny kissing a guy in front of their apartment, he is hurt and feels "rejected." The guys try to convince him to ask a girl out at work and when he's rejected by Leslie Winkle, he is even more depressed.
In the pilot, life is about to change for two geniuses, Sheldon and Leonard when the beautiful Penny moves in across the hall. Leonard sees potential love interest in Penny and offers to retrieve her television from her ex-boyfriend.
Leonard: At least I didn't have to invent 26 dimensions just to make the math come out. Sheldon: I didn't invent them, they are there! Leonard: In what universe? Sheldon: In all of them, that's the point