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Season 4: Episode 24 - The Roommate Transmogrification

The Roommate Transmogrification: ­Bernadette has big news: She completed her PhD! Howard is proud of her, but the rest of the gang razzes him, pointing out that after he and Bernadette get married, they will be known as Mr. and Dr. Wolowitz.

Leonard and Priya's relationship becomes too much for Raj to take when he hears them playing a Star Trek role-playing game so he and Leonard agree to switch apartments until Priya gets her own place.

Sheldon discovers that Raj is a very considerate roommate when he sees Raj dress up the coffee table and use real plates for their dinner. Penny shows up to join them and is surprised to hear that Leonard and Priya are now living together.

When Priya gets a Skype call from her parents, she forces Leonard to hide but during the call, it comes out that Priya is moving back to India. Leonard reveals himself and tells the Koothrappalis he's dating their daughter. They're shocked to find out and Priya doesn't give him a straight answer when he asks if they're breaking up.

Later, we rejoin Sheldon, Raj and Penny in the middle of their dinner. Penny and Raj have both had a lot of wine. Sheldon eventually excuses himself, leaving Raj and Penny alone. They have a heart-to-heart and Penny reveals that she feels like she messed up regarding her relationship with Leonard. Eventually they have an awkward moment but Penny points out they need to remain friends and simply toast to friendship.

The next morning, Leonard is back sleeping on the couch. Wolowitz comes over after having an fight with Bernadette over an expensive gift she gave him. Sheldon comes out of his room, surprised to see Leonard back and all three guys discover a much bigger surprise.