TBBT season 9
Amy breaks up with Sheldon in The Big Bang Theory season 8 finaleCBS

The Big Bang Theory season 9 premieres on 21 September, and the synopsis for the episode is out.

A TVLine report revealed the plot summary which reads as follows:

Brilliant Sheldon is confronted by a mystery of the universe he cannot unravel: when a woman wants time apart to think, exactly how much time does that mean, and is there any way to hurry the process along? In Las Vegas, Penny and Leonard march closer to marching down the aisle, but has Penny gotten over Leonard's infidelity? And if so, will he do anything to un-get her over it?

The season 8 finale ended on a cliffhanger, with Amy breaking up with Sheldon, just as the last moments revealed that he was planning to propose to her. Also, Leonard and Penny were driving to Vegas to get married, but after he confessed to kissing another woman during his time on the North Sea research expedition, Penny is unsure about going through with it.

The Big Bang theory season 8 finale
Will Leonard and Penny marry in Vegas in TBBT season 9?CBS

Season 9 will open with Sheldon trying to unravel the mystery behind how long Amy wants to stay apart from him, and how to shorten the separation. Penny and Leonard will be in Vegas and will be closer to marching down the aisle.

But Will Leonard's infidelity ruin his chances with Amy? According to a new report, the upcoming season will introduce the woman Leonard kissed while on the North Sea expedition.

According to the TVLine report, Melissa Tang will play the character and she will turn up in season 9's second episode.