Amy answers Sheldon's marriage proposal; Howard and Bernadette struggle with unexpected news.
Leonard's job is at stake after he gives an embarrassing radio interview; Amy and Bernadette bond over having to hide their success from Sheldon and Howard.
As Sheldon stresses about picking a wedding date, Amy tries to convince him he has a more laid-back side; Koothrappali and Stuart compete to win the heart of Bernadette's new co-worker.
Wolowitz and Sheldon bond over having disappointing fathers; Leonard is disturbed when his mother finds a new best friend in Penny.
Sheldon and Koothrappali confide in Bernadette when they can't handle Amy and Wolowitz working together; Penny and Leonard learn a secret from an unlikely source about dealing with Sheldon.
Sheldon auditions for the role of the new Professor Proton; Penny takes care of Halley when Bernadette and Wolowitz need bed rest.
Sheldon tries to keep his collaboration with Bert a secret; Penny and Bernadette coach Koothrappali on navigating his relationship with Ruchi.
Leonard and Wolowitz are furious when they learn Sheldon worked with the military behind their backs; Bernadette suspects Ruchi is trying to steal her job.
Sheldon tries to teach the guys a lesson after they cut him out of a potentially valuable investment; a seven-year-old video reveals a secret about Leonard and Penny's relationship.
Sheldon and Amy try to use math to eliminate wedding planning stress; Koothrappali "breaks up" with Wolowitz after realizing he is hurting his confidence.
Sheldon plans an authentic "Little House on the Prairie" dinner for Amy's birthday; Leonard receives a Christmas letter from his brother.
Sheldon and Amy subject their friends to a series of secret experiments to discover which two would be most qualified to be the best man and the maid of honor at their wedding; Penny reveals her true feelings about Amy.
Sheldon kicks Amy out to work solo; Amy and Leonard bond during a series of science experiments; Bert replaces Wolowitz in the band; Sheldon finds Penny a surprising source of scientific inspiration.
Koothrappali learns the woman he's dating has a very upset husband; Sheldon rents his old room for a quiet place to work.
Sheldon petitions Wil Wheaton to appear on the new "Professor Proton" show, but Wil offers a role to Amy instead; Penny gets angry when she thinks the female protagonist in Leonard's novel is based on her.
When Bernadette won't go into labor, her friends try different tactics to get things started; Wolowitz confronts Bernadette after Amy accidentally reveals she's already chosen their son's name.
Leonard jumps through hoops to help secure the perfect wedding venue for Sheldon and Amy; Bernadette and Wolowitz have a hard time deciding who should stay at home with the kids and who should go back to work.
Penny gets the opportunity to host Bill Gates at work when his company wants to partner with hers; Leonard, Koothrappali and Wolowitz do everything in their power to meet him; Sheldon thinks he is the victim of a prank.
Leonard decides to run against Sheldon for president of the tenants association; Bernadette encourages Wolowitz and Koothrappali to find the owner of a drone after they find it in the backyard.
A brilliant but reclusive scientist, Doctor Wolcott, invites Sheldon to his cabin in the middle of nowhere; Penny and Bernadette improvise after Amy doesn't like the tame bachelorette party they planned for her.
Sheldon's comic book store experience changes when writer Neil Gaiman puts Stuart's store on the map; friendships are threatened when Koothrappali takes credit for Penny's astronomical discovery.
Sheldon goes to Las Vegas to win money for science; Penny and Bernadette take Amy wedding dress shopping, but her terrible choice entangles them in a web of lies.
Sheldon's mother won't attend his wedding unless he invites his brother; the Wolowitz kids inadvertently infest Amy, Bernadette, Wolowitz and Koothrappali with pink eye.