The Porkchop Indeterminacy

Plot Summary
Sheldon's attractive twin sister is in town and the guys can't resist hitting on her, while Raj  takes part in a drug trial to surpass his selective mutism.

Extended Plot
Leonard and Raj  notices a flyer for a drug trial that can help with Raj's  selective mutism. They soon bumped into Howard who was peeping into Sheldon's  office. Howard explained there was a very attractive woman  in Sheldon's  office. Soon, Sheldon with the woman  comes out and the gang acts friendly with Sheldon  in an attempt to befriend the woman. Sheldon soon introduced her as Missy ; his fraternal twin sister. Missy makes an interaction with the gang and after Raj's  selective mutism becomes a hindering factor in befriending her he takes up the flyer for the drug trial. Missy explained she was in town because her friend was getting married at Disneyland, since she doesn't have anywhere to stay Leonard  suggested she stay at their apartment and after some convincing, Sheldon  agrees. Back at the apartment, Leonard, Howard and Raj who was now on test drug which surpassed his selective mutism manages to creep Missy  out by hitting on her excessively. Penny rescues her by offering to get her nail done and avoid the boys. Leonard gets sneaky and tells Sheldon  he has to protect Missy's  genetical integrity and only let someone suitable fertilize it in order to produce an individual as remarkable as Sheldon  himself. But ultimately this backfires as Sheldon deemed Howard  and Raj  unworthy and ruled Leonard  out because of his lactose intolerance. When Missy learned of Sheldon's  actions she talked to Sheldon  privately and by the end of it Sheldon  announced that Missy  can date whoever she liked. Leonard, Howard and Raj  decides to hit on her more humanely. Because Leonard won at Wii-Boxing, he also won the right to ask Missy out first, but she turned him down (something they didn't anticipate). Next up, Howard gives it a shot and also failed. Lastly, Raj came by and gave it a go, Missy  seemed to have developed a liking for Raj  but his medication wore off and he was unable to ask her out.

Quotes
[Sheldon's hot twin sister, Missy, is in town for a wedding]

Leonard Hofstadter: If the wedding's not until tomorrow, why don't you stay with us tonight?

Missy: Oh, I don't think so. Shelly doesn't like company. Even as a little boy, he'd send his imaginary friends home at the end of the day.

Sheldon Cooper: They were not "friends". They were imaginary colleagues.

Penny: So, Sheldon's sister is pretty cute.

Leonard Hofstadter: I wasn't staring!

Penny: I didn't say you were; I just said she was cute.

Leonard Hofstadter: Oh! Uh, maybe... if you like women who are tall... and perfect.

Penny: Sheldon, why are you ignoring your sister?

Sheldon: I'm not ignoring my sister. I'm ignoring all of you.

(Leonard wants to sleep with Missy, but Sheldon doesn't let him.)

Sheldon: Here. Eat this cheese without farting and you can sleep with my sister.

(Missy is leaving and Sheldon is saying goodbye to her.)

Sheldon: Well, Goodbye. (Puts his hand out for her to shake.)

Missy: Come on Shelly. (Gives him a hug, which Sheldon does as well.)

Missy: I want you to know I'm very proud of you.

Sheldon: Really?

Missy: Yep. I'm always bragging to my friends about my brother, the Rocket Scientist.

(Sheldon looks in disbelief.)

Sheldon: You tell people I'm a Rocket Scientist?!

Missy: Well yeah.

Sheldon: I'm a theoretical physicist.

Missy: What's the difference?

Sheldon: What's the difference?!

Missy: Goodbye Shelly.

Sheldon: My God! Why don't you just tell them I'm a toll taker at the Golden Gate Bridge! Rocket Scientist, how humiliating!

Trivia

 * This is the second time that Rajesh is able to talk to a girl. Previously it took a large dose of alcohol, this time it's an experimental drug trial.
 * Missy's accent comes and goes throughout the episode.
 * Missy calls Sheldon, Shelly.

Critics
"The humour is pretty solid throughout and should entertain, even though there is a greater opportunity for character development wasted." - The TV Critic's Review