In an upcoming episode of "The Big Bang Theory" season 10, Raj's (Kunal Nayyar) ex-girlfriends will be back to detail what went wrong in his past relationships.

Fans of CBS' popular sitcom will soon be seeing the return of Emily (Laura Spencer), Claire (Alessandra Torresani), Lucy (Kate Micucci), and Emily (Katie Leclerc). As teased in a promotional photo for the episode, Raj's ex-girlfriends will all be huddled together to discuss what went wrong in their respective relationships. Raj's best friend Howard (Simon Helberg) will be there, too.

Meanwhile, Sheldon (Jim Parsons) will be trying to explore his emotions. He will be conducting an experiment using a machine that will help him read and analyze the various types of emotions detected.

Also happening in the episode, viewers will once again see Penny's (Kaley Cuoco) brother Randall (Jack McBrayer). Penny will be setting up a job interview for her brother, and she will be encouraging him to show up. But her ex-convict ex-junkie brother will be having a difficult time acting normal.

"The Big Bang Theory" returns with episode 14, titled "The Emotion Detection Automation," in the first week of February. The show just had a week-long hiatus after airing episode 12, "The Holiday Summation." According to recent reports, the network will once again air an old episode next, following episode 13, "The Romance Recalibration," which aired this week.

To recap episode 13, Leonard (Johnny Galecki) and Penny went through a rough patch in their marriage, when Penny started feeling like her husband has been taking her for granted. And instead of taking Leonard to a spa weekend, she decided to go with Amy (Mayim Bialik). Knowing that his wife was feeling bad, Leonard tried to mend things and did what he could to make it up to her.

"The Big Bang Theory" season 10 airs on Thursdays at 8 p.m. ET on CBS.