The guys are surprised to see a beautiful young woman in Sheldon's office. They are even more surprised when they learn that she is Sheldon's fraternal twin sister, Missy Cooper, who is in town only for two days to attend a friend's wedding. Against Sheldon's wishes, Leonard invites her to stay with them, which she accepts. Leonard, Howard and even Raj (who is participating in a pharmaceutical study, which includes testing a new drug to overcome extreme shyness) fawn over Missy. Using the argument of potential genius offspring, Leonard convinces Sheldon, who abhors physical and emotional contact even with family, that he needs to act brotherly in looking out for Missy's best interests when it comes to finding a suitable boyfriend. Who better in that role than his roommate. Ultimately, the guys come to a solution on who should pursue Missy. But what will Missy have to say about their choice?