The Big Bang Theory, The Celebration Experimentation

Season 9 premiere, Penny has a problem dealing with Leonard's confession about having kissed another woman, while Sheldon is confused about Amy calling a timeout on their relationship.

To ease Penny's mind, Leonard pays a visit to the woman he kissed during his expedition to the North Sea, while Sheldon's breakup with Amy leads him to retaliate by shooting a special episode of 'Fun with Flags'.

The guys surprise Leonard with a belated bachelor-party weekend in Mexico, but their plans hit a bump in the road when they get a flat tyre on the way. Meanwhile, the girls lean on Penny to tell her family that she and Leonard eloped.

Sheldon reverts back to 2003 when he learns that Leonard and Penny are moving in together. Meanwhile Howard and Raj form a band to play at the comic book store.

When Barry Kripke gives the guys fencing lessons, he makes a point of letting Sheldon know he's interested in dating Amy. Stuart has trouble getting female customers at the Comic Book Store, so Penny, Amy and Bernadette stop by to help out.

A helium shortage leads Sheldon and Leonard to do business with a dealer in the black market in order to acquire some of the element for an experiment they need to complete.

Sheldon's interview for a 'Star Trek' documentary focusing on Spock turns up a shocking revelation about his breakup with Amy. Meanwhile, the Wolowitzes haggle over the remodelling of his family home.

When Leonard, Penny and Bernadette learn that Amy is going out on a dinner date, the trio set out to spy on her and the guy. Meanwhile, Sheldon recruits Raj and Howard to find a woman for him.

Now just friends, Sheldon and Amy spend Thanksgiving at the aquarium, a reluctant Wolowitz volunteers at a soup kitchen with Bernadette, Raj and Emily, and Penny realises that Leonard knows a bit more about her than he's let on.

God only knows what song is constantly playing in Sheldon's head, but it reminds him of Amy and leads to a surprising revelation. Meanwhile, she is back in the dating game.

Professor Proton visits Sheldon in a dream and gives him Obi-Wan Kenobi-like advice about whether to go see the new 'Star Wars' film or spend the time with newly reunited girlfriend Amy on her birthday.

Penny entices Leonard to meet with a psychiatrist and the results are surprising, Stuart moves out of the Wolowitz house, and Howard and Bernadette find themselves at a loss.

Dealing with an under-the-weather Sheldon is so draining for Penny, Leonard, and the gang, that they decide to treat themselves to a Sheldon-less weekend.

Sheldon's grandmother, aka Meemaw, visits and there's friction between her and Amy, which intensifies after the elderly woman blurts out a secret about Sheldon.

Sheldon and Amy celebrate Valentine's Day with an episode of Fun With Flags, Leonard and Penny feel the pangs of ageing, and Howard and Bernadette are surprised by what they find in their hot tub.

The gang learns Bernadette is pregnant and celebrates by singing karaoke. Meanwhile, Wolowitz freaks out over the pregnancy announcement and becomes convinced he must make more money to provide for the baby.

Sheldon and the gang celebrate his birthday and he's surprised by a special guest.

Howard reconsiders entering into a legal partnership with Leonard and Sheldon regarding the patent for the infinite persistence gyroscope. Also, the women offer Raj dating advice after Emily reaches out to him following their breakup.

Sheldon shocks Amy with a startling revelation after she buys him a new laptop. Meanwhile, Raj throws Leonard and Howard under the bus after they lie to their wives and sneak off to an early screening of a movie.

Sheldon shares a secret about Leonard when the two go on a weekend trip with Penny and Amy; Raj goes all out with pregnancy gifts.

During a group get-together, a minor argument between Sheldon and Leonard turns into a heated debate, leaving the rest of the gang to choose sides.

Sheldon stays behind to spend quality time with the pregnant Bernadette when the rest of the gang toddles off to a wine-tasting event where they run into Penny's former boyfriend, and Raj introduces his new girlfriend.

When Sheldon decides he'd rather go to a movie screening than hang out with Amy, he hires Stuart to spend the day with her. Meanwhile Leonard's mother visits, and Penny just can't seem to connect with her.

In the Season 9 finale, Leonard's recently divorced parents roll into town, as does Sheldon's holy-roller mother, and all hell breaks loose.