The Roommate Transmogrification

"The Roommate Transmogrification" is the twenty-fourth episode and final episode of the fourth season of the  sitcom The Big Bang Theory. This episode first aired on Thursday, May 19, 2011.

Summary
After Bernadette receives a and gets a well-paying job, the guys make fun of Howard for now having a future wife with a Ph.D while still being the only non-doctor in their group (sans Penny). Meanwhile, Raj becomes Sheldon's new roommate and Leonard moves in with Priya in Raj's apartment.

Extended Plot
Leonard, Sheldon, Howard, Raj, and Priya are at The Cheesecake Factory. Bernadette comes by and announces she is getting her  and the others start to mock Howard about his lack of a Ph.D. and he claims he is not bothered.

At his apartment, Raj hears Leonard and Priya getting ready for fun with a Star Trek . He is troubled by these activities, leaves, and attempts to sleep at Howard's, but Mrs. Wolowitz and her make him uncomfortable.

Sheldon is ting with Amy when he hears a knock on his apartment door. It's Raj wanting to on Leonard's bed. Sheldon discourages it, but finally gives in and asks Raj to sign a and gives him a safety drill. The next morning, Leonard enters his room and sits on his bed; to his surprise he discovers Raj sleeping in it. Raj explains his predicament and asks why Leonard can't sleep with Priya at his apartment, but Leonard says that she doesn't get along with Sheldon. He suggests that until Priya gets her own place in, Raj can stay at Leonard's and vice versa. Raj asks if he can bring girls to Leonard's room, and he agrees because he believes that Raj can't score with a girl and as long as they are there on their own free will.

Later on, Raj gets, arranges it like a fancy dinner, and calls over Sheldon, who is amazed by the presentation. Penny comes over to ask if Sheldon changed his  (the new one now being "pennygetyourownwifi"; no spaces), and she can't help but notice the fancy dinner presentation. Sheldon tells her that Raj has replaced Leonard temporarily and that Leonard is now living with Priya.Howard and Bernadette are in bed together and Bernadette tells him that she got him a present. He opens it and it to find an expensive, and after the teasing from his friends they begin to argue.

Back at the apartment, Sheldon, Penny, and Raj are drinking and having dinner together. After Sheldon leaves to go to bed, Penny continues to talk to Raj, revealing her true feelings for Leonard and admitting that she never should have broken up with him, leaving Raj a little sad. In an attempt to comfort her, Raj tells her that her life is better than his of every night.

Leonard and Priya are making out when her parents call her for a. Priya quickly asks him to go away so her parents don't spot him. Leonard overhears that Priya's moving back to, he feels betrayed and, in the spur of the moment, he reveals himself by telling Priya's parents that they are dating.

The next morning, Penny wakes up and finds herself nude in bed with Raj. She tells him to act as if this hook-up never happened, he just nods as he still can't speak to her sober, which annoys her. Sheldon wakes up and finds Leonard on the couch, moping about Priya leaving for India and breaking up with him. Howard arrives at the door as he had a big fight with Bernadette because of the watch. Suddenly, Penny does the "" out of Leonard's room with Raj close behind her, wrapped in a. She panics and says that "this is not what it looks like" and leaves. Sheldon then asks, "What does it look like?"

Critics

 * The TV Critic "This was an interesting choice for a season finale. It was a mass of developments that many casual fans may have forgotten by next season. In most shows I wouldn't like that but I don't think it will harm The Big Bang Theory much. The show is still working on blending the soap opera in and I think these developments will allow next season to get rolling more quickly. The show remains flawed but funny and contrary to my expectations has improved this season."
 * The A.V. Club gave this episode a B+.
 * IMDb user reviews

Trivia

 * Penny and Raj's night together is later referenced in "The Hook-Up Reverberation" (S8E4), when his girlfriend Emily takes a disliking to Penny because of their "hook-up".
 * Leonard mentions that he and Priya stay at Raj's apartment as she and Sheldon do not get along. This is following the events which occurred during "The Agreement Dissection" (S4E21).
 * Leonard has two Star Wars figures on the stand in his bedroom, first seen in "The Precious Fragmentation". One is a Sideshow Collectibles Heroes of the Rebellion Han Solo in Stormtrooper Disguise Sixth Scale Figure and the other is a 15-inch Kotobukiya Chewbacca Pre-Painted Soft Vinyl Model. The Luke Skywalker in Stormtrooper Disguise Sixth Scale Figure that accompanies the former has been on the bookshelf next to the apartment entryway since "The Vengeance Formulation".
 * The  safety arrows haven't been seen in previous episodes when the lights are off. In the season 5 episode "The Friendship Contraction", this issue is addressed when Sheldon implies that he has removed them, offering the explanation that the emergency glow-in-the-dark paint was wildly .
 * When Raj set the dinner he light some candles. Sheldon does not point out that paraffin candles may contain carcinogenic, unless he assumes Raj's are soy based. Sheldon does make this point in "The Infestation Hypothesis".
 * Leonard finally managed to convince Priya to wear Raj's  uniform mentioned in "The Prestidigitation Approximation".
 * The given to Howard by Bernadette is a Rolex President's, which cost around $25,000 at face value.
 * Sheldon has a new wi-fi password, "pennygetyourownwifi". This action is part of an ongoing joke where Penny keeps using Leonard and Sheldon and Amy's wi-fi without paying. Sheldon makes no real effort to stop Penny from using the wi-fi, other than to criticize her for using it.
 * When Sheldon has Raj sign a temporary, he awards him with an and  that sport the apartment's flag (the latter of which Leonard was "too cool to wear"), but he does not give him a  flag as he did with Leonard. The apartment's flag is a gold lion rampant on a field of azure, as revealed in "The Staircase Implementation".
 * After this episode Howard remains the only person who hasn't seen Penny naked. Sheldon saw her in "The Adhesive Duck Deficiency".
 * Bernadette chooses not to do heart disease research since neither she nor Howard have it, even though in the previous episode Howard says his family is the "history of heart disease". Howard himself has transient idiopathic arrhythmia, as he mentions in "The Middle-Earth Paradigm", so it would seem he is at high risk. Howard mention his arrhythmia again after having sex with Lesley Winkle in "The Cushion Saturation".
 * Last physical appearance of Priya in the show; she makes two subsequent appearances via Skype in Season 5.
 * It really doesn't make much sense that a microbiologist would be studying premature ejaculation as it is not related to an infection.
 * Leonard saying "Open the landing bay doors, shuttle craft approaching!" during sex with Priya is the most explicit sexual reference made in the series thus far.
 * One time Penny does say to herself that Raj looks a lot cuter after she knows how wealthy his family is.
 * In the previous epiosde "The Engagement Reaction", when Mrs. Wolowitz is in the hospital, Howard says that his family is the history of heart disease, and yet Bernadette dismisses the heart research because neither of them have any problems at the present time.

Quotes

 * Raj: I'm the new homo in town. (realizes what he's just said) That came out wrong.


 * Penny: (to Priya about Leonard) Yeah, a little tip, he says he can eat, do not believe it!


 * (Raj arrives at the Wolowitz residence and rings the doorbell. Howard opens the door)
 * Howard: Hey, what's up?
 * Mrs. Wolowitz: IS THAT MY FUTURE DAUGHTER-IN-LAW, THE DOCTOR!?
 * Howard: NO, MOM, ITS RAJ!
 * Mrs. Wolowitz: HE'S A DOCTOR TOO, RIGHT?
 * Howard: YES!
 * Mrs. Wolowitz: LIKE LEONARD AND THAT SKINNY WEIRDO!?
 * Howard: SHELDON! YES, EVERYONE IS A DOCTOR BUT ME!
 * Mrs. Wolowitz: AND WHOSE FAULT IS THAT!?


 * Leonard: [finding Raj sleeping in his bed] What are you doing here?
 * Raj: I was sleeping!
 * Leonard: In my bed?!
 * Raj: Well, I would have slept in my own bed, but it was being used to bring shame to my family... and the memory of Gene Roddenberry!


 * Howard: You got me a Rolex. How much did it cost?
 * Bernadette: You just let me worry about money. (Howard looks up, realizing what she said) I just want my baby to have pretty things.


 * Penny: (In bed with Raj and horrified) OK, this never happened, do you understand??
 * (Raj just nods)
 * Penny: (Annoyed) Really!? Still can't talk to me!?


 * Penny: (entering room disheveled, with a half-naked Raj behind) Damn.
 * Leonard: What’s going on?
 * Penny: Oh. It’s, it’s not what it looks like.
 * Sheldon: What does it look like?