Raj's sister, Priya (Aarti Mankad), was in town for one night on a layover. The back story of this episode involved a five year old agreement that Howard and Leonard made where they promised that nothing would happen between either one of them and Priya. By the evening, Priya had appeared at Leonard and Sheldon's door, while Sheldon was busy with a text based video game.
The 62nd Primetime Emmy Awards took place tonight at the Nokia Theatre in downtown Los Angeles, and like most years, there were few surprises. The Emmy voters tend to be pretty predictable, and tonight was no different, as Mad Men took home Best Drama Series honours and rookie sitcom Modern Family won for Best Comedy Series.
Both Penny and Leonard are feeling the effects of having broken up with each other. To Leonard's surprise, Penny was with a date, as he knocked on her apartment door. Not surprisingly, her date differed quite a bit from Leonard. As a non-genius, he perceived the laser as a weapon and not as a scientific instrument, leading to the clueless dialogue that took place.
After Leonard got into a spat with his room mate, Sheldon, he retreated to Penny's apartment. While they are there, they get into a dialogue that recounted how Leonard and Sheldon first met, leading to multiple flashbacks.
There is a certain type of woman that can go into an established close-knit group of men, insert her sexuality within, and destabilize everything. In this episode of The Big Bang Theory, that woman is Dr. Elizabeth Plimpton. Unfamiliar with the opposite sex, Sheldon used his limited knowledge to prepare for her arrival and stay at his and Leonard's apartment.