"The Big Bang Theory," one of television's most popular comedies, will be back in action Monday on CBS. Fans have been waiting all summer for the Season 9 premiere to check back in with Sheldon (Jim Parsons), Leonard (Johnny Galecki), Penny (Kaley Cuoco-Sweeting) and Amy (Mayim Bialik). But some fans might need a refresher on just where the show left things in the Season 8 finale with its two flagship couples. 

In the Season 8 finale, trouble started brewing for Sheldon and Amy when Sheldon brought up “The Flash” television show in the middle of a hot makeout session on their five-year anniversary. Amy flipped out, pointing out the irony of Sheldon putting so much energy into deciding how he feels about the show while seemingly indifferent about their relationship progressing – the couple had still not slept with each other, even after five years.

Sheldon went to Leonard and Penny for advice, but they told him that they pretty much agreed with Amy that she and Sheldon were taking things a bit slow. Sheldon, though, pointed out the Leonard and Penny were being equally noncommittal, having still not set a date for their wedding. The accusation rattled the couple, who spontaneously decided to drive down to Las Vegas that very night to tie the knot.

However, in the car on the way to Sin City, Leonard confessed that he had kissed someone else a few years ago on a research trip. He wanted to go into their marriage with a clean slate and no secrets, but Penny became worried that he was trying to sabotage their engagement. Fans were left wondering if the wedding would happen after all. 

Meanwhile, back at the apartment, Sheldon Skyped Amy, hoping to make up with his longtime girlfriend. Unfortunately, things did not go as he planned. He was surprised when Amy asked to take some space to figure things out before abruptly hanging up on him. The breakup devastated Sheldon, who pulled out a ring, revealing that he had planned to propose! 

"The Big Bang Theory" goes into Season 9 with some big questions to answer about its two centerpiece relationships. Will Sheldon and Amy reconcile? Will Penny and Leonard actually get married? Fans will find out soon. "The Big Bang Theory" Season 9 premiere airs Monday at 8 p.m. EDT on CBS.

Watch the promo for "The Big Bang Theory" Season 9 below: