The Roommate Transmogrification

During another night out at the Cheesecake Factory, the guys and Penny make fun of Leonard because of his lactose intolerance. However, when Bernadette announces that her dissertation has been accepted, earning her a Ph.D. and a well-paid job, Leonard seizes his chance and starts to mock Howard with the other guys, degrading him for being the only non-doctor in their group. Later, Bernadette decides to buy Howard an expensive Rolex watch as a present and tells him to "let her worry about the money", a comment that deeply disturbs Howard.

Meanwhile, Leonard's and Priya's noisy and "scientifically inaccurate" sexplay in his apartment annoys and disgusts Raj. When Priya wears his Halloween Lieutenant Uhura costume during a Star Trek sex fantasy, Raj leaves and spends the night at Sheldon's apartment. When Leonard finds Raj in his bed the next morning, he apologizes for using the latter's apartment, and proposes that Raj moves in with Sheldon until Priya finds her own place. Raj immediately takes a liking to the idea, and, after Sheldon's usual bureaucratic procedures (including a modified "temporary roommate agreement" and a will), moves in with him. Raj then prepares a fancy dinner to ingratiate himself with Sheldon, who is delighted.

Penny comes over to ask for their Wi-Fi password, because she does not want to pay for her own, and then stays for dinner. She and Raj both get drunk from the wine Raj serves. When Sheldon starts to get annoyed by them and opts to go to bed, Penny tells Raj that she "screwed up", that she should not have broken up with Leonard, and that she would be "on" him (Raj) if they were not friends.

Priya receives a video call from her parents and orders Leonard to hide in the bedroom, because she still does not want them to know that she is dating him. Leonard overhears the Koothrappalis talking about Priya moving back to India the following month. When he storms back into the room to confront her, he reveals to her parents that they are in a relationship (justifying that her moving back to India would certainly mean they are breaking up, leaving it moot if her parents know).

At the end of the episode, Sheldon discovers Leonard sleeping on the couch at their apartment, because he is still mad at Priya, just before Howard shows up and announces that he had a fight with Bernadette over the watch. Penny wakes up in Leonard's room and is horrified when she wakes up naked with Raj and realizes she hooked up with him. She tells him that "last night never happened." Raj nods his head and Penny is peeved that he still cannot talk to her even though they slept together. Penny tries to sneak out of the apartment; however, Raj wrapped in a comforter and Penny emerge from Leonard's room, right in front of everyone. Penny just states that "it’s not what it looks like," which leaves Leonard and Howard confused. Sheldon asks, in all sincerity, "What does it look like?"

On the night of its first broadcast on May 19, 2011, the episode was watched by 11.30 million households.[2] The episode was the fourth least watched episode of the season, despite it being the season finale.

IGN's Jenna Busch gave the fourth-season finale a positive review stating that "For the most part, the episode was strong". Busch did, however, criticise the cliff-hanger of the episode by stating: "a Penny/Raj hookup just seemed a bit off. Even if you were fine with that, the ending still seemed kind of soft to me". Busch then complimented the show's season by saying "there have been so many great moments throughout this season. Even when I've critiqued the show, there has always been something to love. I can't wait for next season to start".[3]

Carla Day from TV Fanatic gave the episode an extremely positive review by saying "I found the installment and each of the stories to be hilarious and/or to propel the characters forward. Overall, as a season finale, it gave me the laughs I expect and left me sitting in anticipation for the show to return in September". Day did give the cliff-hanger a mixed review by writing "At first, I thought it was pretty funny, but now, I think it is just sad" and "I'm going to wait until the show returns and I can see how it all plays out before I decide if I like this new entanglement or not". Day then praised the season as a whole and complimented the three new female characters by saying "Overall, I thoroughly enjoyed this season, in particular, the growth of our nerdy friends and the addition of Bernadette, Amy and even Priya to the mix".[4]

• "The Roommate Transmogrification" on IMDb
• "The Roommate Transmogrification" at TV.com