The Big Bang Theory
The Big Bang TheoryCBS

Monday's episode of "The Big Bang Theory" will see Leonard trying to sort out his issues with Penny, who in the previous episode, was still upset that her husband kissed another woman during his North Sea voyage a few years ago.

The second episode of season 9, titled "The Separation Oscillation", will introduce Mandy, the woman Leonard kissed, and he will attempt to prove that their kiss was just a spur of the moment decision and that it doesn't mean he has feelings for Mandy.

The synopsis of "The Separation Oscillation" reads:

Leonard confronts the woman he kissed on the North Sea in an attempt to set Penny's mind at ease. Also, Sheldon films a special episode of "Fun with Flags" after his breakup with Amy, and Bernadette feels guilty about withholding a secret from Penny.

Towards the end of the episode, Penny and Leonard would have reconciled and it won't be long before they decide to move in together.

According to the synopsis of "The 2003 Approximation", the fourth episode of the ninth season, Sheldon won't be happy when the newly married couple decides to take the next step in their relationship.

Sheldon is someone who hates change, and will bring out the Roommate Agreement to ensure that Leonard doesn't disrupt their current lifestyle. An extended plot summary of "The 2003 Approximation" also hints at Sheldon asking Amy to move in with him.

"The Roommate Agreement will be around and out and on the table and being discussed in the fourth episode," showrunner Steve Molaro told The Hollywood Reporter. "Sheldon is not happy about a lot of things that are going on in his life right now. But he's doing his best to try and hold it together and get past it all: Rise above it or solve it. It's a lot of weird things that he knows he's a smart guy and he's used to being able to apply logic and science to figuring things out and none of that seems to be working for him these days."

"The Big Bang Theory" airs Mondays on CBS.