When Penny breaks up with her boyfriend, Leonard finally gets up the courage to ask her out on a real date. When she says yes, each seeks the "wisdom" of a reluctant advisor -- Sheldon.

When Penny breaks up with her boyfriend, Leonard finally gets up the courage to ask her out on a real date. When she says yes, each seeks the "wisdom" of a reluctant advisor -- Sheldon.

When Penny learns that Leonard doesn't celebrate birthdays, she attempts to throw him a surprise party; she is sidetracked by Sheldon, however, who unexpectedly gets to live out one of his greatest fantasies at an electronics store.

Leonard, Wolowitz, and Koothrappali all become smitten with Sheldon's twin sister, Missy (guest star COURTNEY HENGGELER), and Leonard devises a plan to eliminate his rivals. The plan backfires, however, when Sheldon declares he will decide whom his sister dates.

When Leonard and the guys buy a time-machine prop from a classic 1960 movie, its arrival creates problems for Penny, and she tells the boys that their obsession with comics and toys is "pathetic."

The guys decide to compete in the university's Physics Bowl, but since Sheldon's only focus is to prove his mental superiority, the guys kick him off the team. To take his spot, they enlist his nemesis Leslie Winkle (recurring guest star SARA GILBERT).

When Leonard and Sheldon meet a 15-year-old physics prodigy, Sheldon is distraught that this boy genius is younger and smarter. In an attempt to restore a sense of purpose, the boys come up with a solution to derail the young prodigy's research.

Sheldon is sick, and Leonard and the guys sneak out to a "Planet of the Apes" movie marathon to get out of taking care of him--which leaves Penny as the only person to whom the needy Sheldon can turn.

After hearing Penny sing, Leonard lies to avoid seeing her perform. Sheldon goes one step further with a more elaborate lie, leading to the appearance of his nonexistent cousin. D.J. QUALLS ("Road Trip") guest stars.

Leonard and Sheldon's friendship is put to the test when Leonard wants to present a paper they co-authored at a physics convention, but Sheldon does not.