Bernadette and Howard discuss where their relationship is heading when Howard once again can't stay the night since he has to look after his mother. When Bernadette broaches the topic of them moving in together, Bernadette ultimately gives Howard an ultimatum: her or his mother. When she asked him this question, she didn't anticipate what Howard wants in a house-mate, sexual partner or not. Meanwhile, Raj's sister Priya is back in town on business. Knowing that Leonard and Priya had casual sex last time she was in town with Leonard wanting their relationship to progress further, Raj refuses to let Leonard see or speak to Priya. But Priya and Leonard do speak, and much to Raj's anger, they decide to start seeing each other. But one other person may be affected by Leonard and Priya dating: Penny. Although Penny outwardly says she is happy for Leonard, Amy, as her new BFF, wants to provide some comfort to Penny, all the while gathering some scientific data.