Leonard gets upset with Sheldon when he spoils the ending of one of the Harry Potter books for him, so he storms over to Penny's place to cool off. While there, he broaches the subject of moving in with Penny, which she isn't ready for and can't articulate properly. Unable to properly convey her feelings to Leonard, he plans on moving in, which gives Amy the opportunity to move in with Sheldon. Penny and Sheldon talk the apartment situation over and discover they're both against having their significant others move in, so decide they have to be honest about their feelings. When Sheldon talks to Amy, he winds up selling Penny out, saying that it's all her fault because she doesn't want Leonard to move in. Amy confronts Penny and Leonard overhears it, forcing Penny to tell him she's not ready to take that step with him yet. Meanwhile, Wolowitz is going to Vegas with Bernadette, so he asks Koothrappali to keep an eye on his mother, since she's dealing with a break-up with her lover, the dentist. Wolowitz' mother puts a big guilt trip on him and forces him to stay, to the point where he has to try and sneak out of the house to get away.
