Penny tries to seduce an abstaining Leonard to ruin his “donation” for her ex-boyfriend, Zack, and his wife, Marissa. Also, Wolowitz, Bernadette, Anu and Koothrappali turn Koothrappali’s canceled bachelor party into a couple’s trip.

Sheldon is thrilled to help Bernadette and Wolowitz navigate bureaucratic paperwork, until he discovers they are breaking the law. Also, Leonard is disappointed when his friends exclude him from a scientific project.

Sheldon and Amy are thrilled when their super asymmetry theory is proven by two physicists, until they try to kick Amy off the Nobel nomination; Bernadette has a big success at work.

Penny’s ex-boyfriend, Zack, and his wife want a baby, but when Zack is infertile, they ask Leonard for help. Also, Koothrappali attempts to mend things with his ex-fiancée, Anu.

Penny and Leonard organize a paintball game that results in mayhem when Sheldon is jealous of Amy. Also, Koothrappali catches Anu with her ex-boyfriend, and Stuart doesn’t want to move in with Denise.

Sheldon and Amy are still down about their theory being disproven, but a VHS tape from Sheldon’s past inspires him not to give up. Bernadette turns into a pageant mom when she tries to help Howard ace his Magic Castle audition.

Sheldon and Amy are devastated after learning from a Russian paper that Super Asymmetry has already been discovered and disproven. Ultra-competitive Bernadette asks Stuart’s girlfriend to teach her how to beat Howard in a popular video game.

Sheldon tries to bond with Amy’s father, but when Howard lures Mr. Fowler away with magic tricks, Sheldon has no choice but to bond with Mrs. Fowler. Raj and Anu try to get physical for the first time.

Leonard is caught between a rock and a hard place when he’s responsible for distributing extra grant money. Bernadette turns the backyard playhouse into a hideaway from Howard and the kids.

When Howard dresses up as Sheldon for Halloween, Sheldon seeks retaliation at Leonard and Penny’s Halloween party. Leonard is shocked that Penny doesn’t remember their first kiss.

When Amy doesn’t have time to work on super-asymmetry, Sheldon goes to great lengths to ensure she’s available to work with him even it if means accidentally sabotaging her career in the process. Raj doesn’t want Howard to join him in hosting a show at the planetarium.

When Sheldon won’t tell anyone why he’s never mentioned his childhood best friend, Leonard takes matters into his own hands. Bernadette and Penny take out Raj’s fiancée for dinner to get the skinny on her.

The Wolowitzes’ life gets complicated when Stuart starts bringing his new girlfriend home. Penny and Leonard talk about starting a family. Raj explores an arranged marriage.

Sheldon and Amy drive themselves crazy trying to figure out what ‘perfect gift’ Leonard and Penny gave them for their wedding. Raj decides he wants to settle down and asks his father to arrange a marriage for him.

Sheldon and Amy’s honeymoon runs aground in New York. Penny and Leonard discover they are uncomfortably similar to Amy’s parents. Raj insults physicist Neil deGrasse Tyson and starts a Twitter war.

When Amy’s parents and Sheldon’s family arrive, everybody is focused to make sure all wedding arrangements go according to plan – everyone except the bride and groom.

When Sheldon learns that his mother won’t attend his wedding unless he invites his brother, Georgie, he and Leonard travel to Texas to end a family feud. Also, the Wolowitz kids inadvertently infest Amy, Bernadette, Wolowitz and Koothrappali with pinkeye.

Sheldon goes to Vegas to win money for science. Also, Penny and Bernadette take Amy wedding dress shopping, but her terrible choice entangles them in a web of lies.

Sheldon’s comic book store experiences changes when writer Neil Gaiman puts Stuart’s store on the map. Also, Koothrappali takes credit for Penny’s astronomical discovery, and friendships are threatened.

A brilliant but reclusive scientist, Doctor Wolcott, invites Sheldon to his cabin in the middle of nowhere, and Leonard, Raj and Howard go along for the trip. Also, Penny and Bernadette improvise after Amy doesn’t like the tame bachelorette party they planned for her.

When Leonard learns Sheldon is the president of the tenants association, he decides to run against him. Also, Bernadette encourages Wolowitz and Koothrappali to find the owner of a drone after they find it in the backyard.

Bill Gates visits Penny’s work, and the gang schemes to meet him. Hilarity ensues.

Leonard jumps through hoops to help secure the perfect wedding venue for Sheldon and Amy. Also, Bernadette and Wolowitz have a hard time deciding who should stay at home with the kids and who should go back to work.

When Bernadette won’t go into labor, the gang tries different tactics to get things started. Howard confronts Bernadette after Amy accidentally reveals she’s already chosen their son’s name.

Leonard’s book raises questions, and Amy guest stars on the new Professor Proton show.

Koothrappali finds himself in the middle of domestic drama when he learns the woman he’s dating, has a very upset husband. Also, when Sheldon rents his old room back for a quiet place to work, he drives Leonard crazy by being a model tenant.

When Sheldon kicks Amy out to work solo, she and Leonard bond during a series of science experiments. Also, Bert the geologist replaces Wolowitz in the band Footprints on the Moon, and Sheldon finds Penny a surprising source of scientific inspiration.

Sheldon and Amy will try to use science to see who should be their Maid of Honor and Best Man.

Sheldon and Wolowitz plan birthday celebrations for Amy and Halley, respectively. Also, Leonard get a Christmas letter from his brother that causes him to spiral out about his own lack of accomplishments.

Sheldon and Amy try to eliminate stress from wedding planning by applying math to the process. Also, Koothrappali “breaks up” with Wolowitz after realizing his best friend is actually hurting his confidence.