Penny has the role of Mimi in a one-day workshop stage production of Rent, and asks Leonard and Sheldon if they want to go see her perform. Based on hearing Penny sing badly, Leonard and Sheldon decline, with Leonard even lying to her to get out of it. Sheldon is feeling uncomfortable in being a part of Leonard's lie, so he takes proactive measures to get out of that lie. Sheldon's actions don't hurt Penny but rather confuse Leonard. But Sheldon takes his proactive measure to the extreme, utilizing the hidden talents of Toby Loobenfeld, a research assistant in the particle physics lab.

Leonard finds a letter in the trash can, the letter an invitation for him and Sheldon to speak at an upcoming conference on the topic of their latest joint research findings. Sheldon threw the letter out since he didn't want to do it. This brings to the forefront several issues. Has Sheldon thrown out any other important letters to Leonard? Who has the right to their joint intellectual property, especially if Leonard wants to present? Whose idea was the research to begin with? In Penny's eyes, does Leonard own anything appropriate to wear to the conference? Can Leonard and Sheldon come to a compromise so that they will speak to each other and be friends again?

When Raj's parents set him up on a blind date, he finds he can talk to women with the aid of alcohol.

When Howard hooks up with Penny's old friend, his absence in the gang causes problems for the rest of the guys.

The guys are invited to Penny's Halloween party, where Leonard has yet another run-in with Penny's ex-boyfriend Kurt.

Leslie seduces Leonard, but afterwards tells him that she is only interested in a one-night stand.

Sheldon's mother is called to intervene when he delves into numerous obsessions after being fired for being disrespectful to his new boss.

Leonard gets upset when he discovers that Penny is seeing a new guy, so he tries to trick her into going on a date with him.

Penny is furious with Leonard and Sheldon when they sneak into her apartment and clean it while she is sleeping.

A pair of socially awkward theoretical physicists meet their new neighbor Penny, who is their polar opposite.

Come join Kat & Paul as they discuss this wonderful 1st episode.