Sheldon and Leonard are two brilliant, but socially inept theoretical physicists who share an apartment. In the series premier, they meet their new neighbor, Penny, a stereotypical beautiful dumb blond. In spite of the obvious hopelessness of the situation, Leonard is utterly smitten.

Leonard agrees to sign for a package for Penny, but when it turns out to be a massive unassembled entertainment unit, he and Sheldon must muscle the box up several flights of stairs - a task for which they are ill-equipped. Once in Penny’s apartment, Sheldon is appalled at Penny’s housekeeping practices and takes it upon himself to clean up somewhat until Penny gets home. That night, the fuss budget in him can’t stand it anymore, so he sneaks back to finish the job (while Penny is asleep). Against his better judgement, Leonard helps. When Penny wakes to find that the guys were in her place, she feels violated and is furious, setting back Leonard’s plans for romantic bliss.

Leonard is crushed when he sees Penny kissing another man in the hallway. Faced with the bleak reality of his chances with Penny, he turns his affections toward Leslie, a fellow scientist at the university. His advances, while partially successful, are less than satisfying. While Sheldon sees no possible future for Leonard and Penny, he feels sympathy for Leonard and suggests that he ask Penny on an actual date.

When Sheldon is fired, he tries to explore life outside the university. He goes food shopping with Penny, who is less than enthusiastic, and then conducts several scientific experiements in his apartment. When Leonard goes as far as buying a loom and weaving ponchos, Leonard decides to call Sheldon’s mother for help.

Leslie invites Leonard to play cello in a musical ensemble, but they have to practice at the guys’ apartment. Once practice is over, Leslie quickly seduces Leonard for a sexual encounter. Having absolutely no experience around anyone who has actually had sex, Sheldon seeks wisdom from Penny. In spite of initial trepidation, Sheldon decides that Penny’s restaurant has a superior hamburger and will be a regular stop for him.

When the guys are invited to Penny’s Halloween party, Leonard sees it as an opportunity to get to know her friends and thereby get closer to her, but when her ex-boyfriend arrives, those plans take a turn for the worse. However, the evening isn’t without its positive aspects for Leonard. Or for Rajesh.

Wolowitz seduces a friend of Penny’s. As they have taken over Penny’s apartment, Penny is forced to sleep on Leonard and Sheldon’s couch. The guys are also short one member on their HALO team, and they ask Penny to join them.

Koothrappali is overwhelmed after his parents arrange a blind date, but he discovers he actually can talk to the opposite sex after a few drinks; however, complications set in when his beautiful date is more interested in Sheldon.

Sheldon and Leonard are asked to present their work at a physics conference together, but a fight ensues when Sheldon refuses to share the honor. When Penny steps in to mediate, things only get worse.

Leonard tells Penny a lie so that he doesn’t have to hear her sing again, while Sheldon widens the lie, which makes Leonard in need to produce a phony cousin.

Penny nurses a sick Sheldon back to health, unaware that the guys refuse to do so because he makes such a lousy patient.

Leonard and Sheldon meet a 15-year-old physics prodigy and Sheldon is thrown off that the boy is younger and smarter than himself. This leads the boys to try to come up with a way to restore Sheldon’s sense of self and ultimately decide to try to throw Dennis’ research.

Sheldon finds himself out of the gang’s Physics Bowl team and replaced with Leslie. Not taking this sitting down, Sheldon decides to start a team of his own to prove that he’s the best out of the gang.

Leonard and the gang buy a time machine prop that was used in a classic 1960s movie. However, their thrill over having a replica time machine is shot down when Penny tells them that their obsession with comics and toys is pathetic.

The guys fight for Sheldon’s twin sister when she arrives for a visit, but Leonard has a plan to get rid his rivals. Sheldon becomes her protector and decides he will pick out who she will go out with, despite her disapproval.

Penny throws Leonard a surprise party after discovering that he doesn’t celebrate birthday’s, but becomes sidetracked by Sheldon, who, while at an electronics store, gets to live out one of his greatest fantasies.

Leonard and Penny each seek a reluctant adviser, Sheldon, for a bit of wisdom concerning their date with each other.