Leonard asks Raj how things are going with the woman he's dating, and Raj says that they broke up. The guys point out the bad luck Raj has with dating, and Sheldon fails at trying to make him feel better. 

Bernadette tells the group about an emotion detecting machine she read about, and Howard thinks he could get a prototype for Sheldon to try.

Meanwhile, Penny tells Leonard that her brother is coming to stay with them while he takes a job interview at her work, and if it goes well, he might actually stay for a while.

Sheldon gets the prototype which seems to work well, and he quickly points out Leonard is angry about Penny's brother coming to visit, even though Leonard insists he's fine with it.

As Leonard and Penny argue, Sheldon quickly gets caught in the middle

Raj gets together with his old girlfriends for a "focus group" to find out why his relationships don't work out, and he gets a lot of criticism.

Sheldon is surprisingly emotional about the trouble the machine has caused, and more so about the fact that he's so bad at understanding emotion. Amy makes him feel better, and Leonard and Penny eventually apologize to him.