The four boys have just returned from RenFaire, but Sheldon is complaining about the many historical inaccuracies. Penny is dating again, much to Leonard's shagrin.
There's a hilarious reference to Raj having made out with an Orion slave girl at ComicCon who turned out to be a guy. I've seen a guy dressed as slave Leia, so that doesn't surprise me in the least. And Raj must have really been drunk to have been able to make out with who he thought was a girl.
Leonard tries to get back into the dating scene again, and Leslie proposes that they hook up again. She's apparently no longer into meaningless sex, so they arrange a date. She starts off conversation with asking how many children they should have, but Leonard thinks that's moving too fast. So then she asks what genetic defects he has.
At the end of the date, Leonard is seeing Leslie out of his apartment just as Penny is returning from her date with her guy, and both Leonard and Penny try to outdo the other in kissing their dates goodnight.
It was funny for them to reference a joke from last season where Sheldon explained Schrodinger's cat to Penny, and as Penny and her date were coming up the stairs, she was apparently at the tail end of explaining it to him. It was even funnier when he thought she was talking about a character from Peanuts.
Because Leonard wants privacy on his dates with Leslie, Sheldon is relegated to playing Mario Bros. on a simulator on his keyboard while sitting on the stairs since he apparently can't go to the movies or dinner by himself. Sheldon also doesn't like Leslie because he doesn't respect her work but also because she says mean things to him, like calling him "dumbass".
Sheldon finally gives in and gives his blessing on their relationship but inadvertently ends up highlighting a major difference of opinion between Leslie and Leonard on a physics point, and Leslie doesn't see how they can have a relationship that way. (It's kind of like the parents being from two different religions.)
The boys talk Sheldon into going back to RenFaire so they can see scantily-clad women, and Sheldon is dressed as Spock observing a time anomalous planet/culture.