Leonard is happy to meet new neighbor Penny, but his roommate thinks he is chasing an impossible dream.
Leonard volunteers to sign for a package, hoping to make a good impression on Penny.
Unhappy to learn that Penny is seeing someone, Leonard summons the courage to ask another woman on a date.
Getting fired gives Sheldon the opportunity to explore life beyond physics, but when he spends his time weaving ponchos and acting like a shut-in, Leonard calls Sheldon's mother for assistance.
Leonard, realizing his pursuit of Penny is fruitless, has an unexpected encounter with a fellow scientist (Sara Gilbert).
Leonard, Sheldon, Wolowitz and Koothrappali attend Penny's Halloween party.
Penny sleeps on Leonard and Sheldon's couch when Wolowitz seduces her friend and takes over her apartment; in need of a fourth member, the guys ask Penny to join their "Halo" team.
On a blind date, Koothrappali discovers that he can talk to the opposite sex after a few drinks, but his date takes an interest in Sheldon.
Penny tries to mediate when Sheldon and Leonard disagree on whether to present their joint findings at a physics conference.
Leonard and Sheldon try to avoid seeing Penny perform after hearing her sing, but the elaborate lie Sheldon tells leads to an unexpected result.
Leonard and the boys avoid Sheldon when he gets sick, leaving Penny to nurse him back to health.
Sheldon and Leonard look for a way to derail a 15-year-old physics prodigy's research.
When Sheldon tries to prove his mental superiority as they train for the Physics Bowl, the guys kick him off the team and bring his nemesis (Sara Gilbert) aboard.
Leonard and the guys buy a time machine prop from a classic movie; Penny tells the guys their obsession with comics and toys is pathetic.
Leonard devises a plan to eliminate his rivals when he, Wolowitz and Koothrappali all fall for Sheldon's twin sister, but his plan backfires when Sheldon decides to choose who his sister dates.
Penny learns that Leonard does not celebrate birthdays, so she plans a surprise party; Sheldon unexpectedly gets to live out one of his biggest fantasies in an electronics store.