Brilliant physicist roommates Leonard and Sheldon meet their new neighbor Penny, who begins showing them that as much as they know about science, they know little about actual living.
Leonard volunteers to sign for a package in an attempt to make a good impression on Penny, but when he enlists Sheldon for help, his attempt at chivalry goes terribly awry.
Leonard asks a woman out after he finds out that Penny is seeing someone.
Sheldon's getting fired forces him to explore what life has to offer outside physics, leaving Leonard to take drastic action to snap his friend out of his funk.
Fearing he's wasting his time on Penny, Leonard ends up making a connection with Leslie. Meanwhile, Sheldon frets over a change to his hamburger routine.
Penny hosts a Halloween party, putting Leonard, Sheldon, Wolowitz, and Koothrappali through a new test of their social skills.
With Wolowitz AWOL with one of her friends, Penny's recruited to fill in for him on the guys' Halo team.
Raj's parents set him up on a blind date, and when he discovers he can talk to her, she shows interest in Sheldon.
When they're invited to present at a physics conference, Sheldon's reluctance to share the credit leads to a tiff between he and Leonard, and Penny's intervention only exacerbates the situation.
Leonard and Sheldon each lie to avoid hearing Penny sing in a production of Rent. However, Sheldon's lie becomes a bit too complicated for its own good.
With his friends knowing how sour he acts when sick—and avoiding him as a result—Sheldon is nursed for by Penny, who hasn't a clue what she's in for.
With Sheldon rattled and impossible to be around after meeting Dennis, a 15-year-old physicist who's smarter than he, the rest of the guys search for a way to eliminate the threat.
Sheldon finds himself booted from the gang's Physics Bowl team and replaced with Leslie, so he forms his own team, hoping to prove he's superior.
When the delivery of a full-size prop of 1960's The Time Machine makes Penny miss work, she scolds Leonard about his sci-fi collectibles. He decides it's time to give up such childish pursuits.
The rest of the gang fall for Sheldon's twin sister, and Leonard's plan to win her heart is derailed when Sheldon declares he'll be the one to decide who can date her.
Penny wants to throw a surprise party for Leonard, but Sheldon's indulgence at an electronics store throws her off-track.
Penny's break-up spurs Leonard to summon the courage to ask her out, and each goes to Sheldon for advice on their upcoming date.