The Big Bang Theory
Raj (Kunal Nayyar, right) and the gang plan on leaving Sheldon (Jim Parsons, left) out of a Las Vegas trip in episode 13 of "The Big Bang Theory" Season 9. CBS

Sheldon (Jim Parsons) and Amy (Mayim Bialik) are back together, but for the past few episodes of "The Big Bang Theory" Season 9, Amy has been away at a conference in Michigan. Well, apparently that extended absence is no coincidence. When Sheldon reaches out for advice in a sneak-peek video for episode 13, "The Empathy Optimization," the teaser reveals the real reason Amy has been gone so long.

According to the synopsis for episode 13, Penny (Kaley Cuoco), Leonard (Johnny Galecki), Bernadette (Melissa Rauch), Howard (Simon Helberg), Raj (Kunnal Nayyar) and Emily (Laura Spencer) decide to head to Las Vegas for the week on a party bus! However, they plan on leaving Sheldon, who has had a bad attitude lately (and a bad cold), behind. Sheldon does not want to be left out, so he decides to go on an apology tour, saying sorry to each of his friends individually, in the hopes of getting them to change their minds about the trip.

However, before his big apology tour, Sheldon calls Amy via Skype to figure out just why everyone is so peeved at him.

"You know how when you are sick you are allowed to be cranky and say whatever you want and other people's feelings don't matter? I had a 101 fever. If that is not a time to verbally abuse my loved ones, when is?" asks a frustrated Sheldon.

Amy responds with some brutal honestly.

"Sheldon, when you are sick, you can be unbearable," she tells her stubborn boyfriend. "That is why your friends have been known to work late, or sneak out to the movies, ... or stay at neurobiology conference three days after it has ended."

So, the reason Amy has been in Detroit for so long is she did not want to deal with Sheldon! He can not believe it, but Amy quickly ducks out of the awkward conversation.

"Oh, I just heard something. It might be hail, it might be gunfire. Either way, I'm going to go take pictures. Bye!"

Watch the sneak-peek video for episode 13 below:

Will Amy's advice help Sheldon with his apology tour plan, or will the gang go to Las Vegas without him? Fans will have to wait to find out. "The Big Bang Theory" airs Thursdays at 8 p.m. EST on CBS.