After a pipe bursts in Amy's apartment, Penny and Leonard invite her to stay with them until the problem is fixed. Penny suggests that Amy stay in Leonard's room and that Leonard stay in Penny's apartment.

This means that essentially, Amy and Sheldon would be moving in together -- just temporarily.

Sheldon is hesitant, but Amy convinces him by saying they can treat it as an experiment to collect data on their relationship.

To make the experiment more valid, they decide to switch apartments with Penny instead. That means they'll also be sharing a bed.

Meanwhile, Bernadette and Howard (and Raj) return from a visit to the doctor with an ultrasound of a healthy baby. Bernadette and Howard have decided to let the baby's sex be a surprise, but Raj reveals that he knows because he saw the folder.

Sheldon and Amy start getting settled in Penny's apartment, and Sheldon struggles to decide which side of the bed to sleep on.

While Howard and Bernadette struggle with whether or not they want to ask Raj the sex of the baby, Sheldon's sleeping habits keep Amy awake, and Leonard and Sheldon enjoy the apartment to themselves by dancing around in their underwear.