Sheldon and Amy's honeymoon runs aground in New York; Penny and Leonard discover they are uncomfortably similar to Amy's parents; Koothrappali insults physicist Neil deGrasse Tyson and starts a Twitter war.
Sheldon and Amy go crazy trying to figure out what "perfect gift" Leonard and Penny gave them for their wedding; Koothrappali decides to settle down and asks his father to arrange a marriage for him.
Sheldon is thrilled to help Bernadette and Wolowitz navigate bureaucratic paperwork, until he discovers they are breaking the law; Leonard is disappointed when his friends exclude him from a scientific project.
Penny tries to throw a wrench into Leonard's plan to be a sperm donor for her ex-boyfriend; Wolowitz, Bernadette, Anu and Koothrappali turn Koothrappali's canceled bachelor party into a couple's trip aboard the "vomit comet."
The gang uses deception and betrayal to make it to the one open seat at Wil Wheaton's celebrity Dungeons and Dragons game with William Shatner, Joe Manganiello, Kareem Abdul-Jabbar and Kevin Smith.
When Penny and Bernadette go to San Diego for a pharmaceutical sales convention, Wolowitz is left in charge of the kids; Sheldon finds a book about experimenting on kids.
When competitors Pemberton and Campbell charm America on a publicity tour, Sheldon and Amy try to win over Nobel laureates Kip Thorne, George Smoot and Frances Arnold; Halley's fear of the dark leads to opportunity and conflict.
The weight of winning a Nobel Prize weighs heavy on Amy's shoulders; Koothrappali and Wolowitz try to relive the good old days after Wolowitz buys a scooter that looks like the one he had years ago.
Koothrappali is worried people won't take him seriously in his own field after publishing a paper that suggests he may have discovered alien life; Leonard wants to be the principal investigator on a plasma physics study.
Kripke has proof that Dr. Pemberton plagiarized his thesis in college, and Sheldon and Amy aren't sure if they should turn him in or not; Wolowitz learns that Bernadette wasn't the only waitress at the Cheesecake Factory who had a crush on him.
Leonard is pleasantly surprised when Beverly comes to visit and she's genuinely kind to him, until he finds out the real reason she's there; Denise and Stuart overstay their welcome at the Wolowitz house.
Sheldon and Amy await big news.
Bernadette and Wolowitz leave their kids for the first time; Penny and Leonard try to keep a secret; Sheldon and Amy stick together; Koothrappali makes a new friend; the gang travels together into an uncharted future.
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.
When Amy's parents and Sheldon's family arrive, everybody is focused on making sure the wedding arrangements go according to plan -- everyone except the bride and groom.
When Sheldon must teach a class, Howard decides to take it; Amy takes advantage of the tension between Penny and Bernadette.
Wolowitz feels nervous when he is asked to throw the first pitch at a Los Angeles Angels game; Penny and Leonard want to prove Sheldon wrong after he says he and Amy are the better couple.
Raj's honesty comes back to haunt him when his new girlfriend is unfriendly to Penny; the guys think about becoming part owners in Stuart's store.
During their weekend in Las Vegas, Bernadette and Amy accuse Penny of being a buzz kill; the guys try to invent the next big thing.
Raj and Sheldon try to simulate a dark-matter research expedition; after a fight about money, Penny and Leonard turn to Bernadette and Wolowitz for advice.
The guys try to help when Penny is faced with an awkward dilemma at work; Bernadette and Amy discuss sexuality and female scientists.
Sheldon feels pressured to participate in romantic traditions when the gang re-creates a high-school prom on the roof.
Sheldon gives spontaneity a try, which causes unexpected friction for Penny, Bernadette and Amy; Raj asks Howard for help with preparation for a date with Emily.
Professor Proton (Bob Newhart) helps Sheldon deal with grief; Leonard gets into a competition with Penny; Bernadette and Amy prepare a "Star Wars Day" gift for the guys.
A bad day compels Penny to re-evaluate her choices -- including Leonard; Bernadette and Howard must care for Mrs. Wolowitz; Sheldon gives Raj advice on relationships.
Faced with an uncertain future, Sheldon considers a major change; Emily and Raj decide to take things to the next level.
Leonard is happy to meet new neighbor Penny, but his roommate thinks he is chasing an impossible dream.
Leonard volunteers to sign for a package, hoping to make a good impression on Penny.
Unhappy to learn that Penny is seeing someone, Leonard summons the courage to ask another woman on a date.
Getting fired gives Sheldon the opportunity to explore life beyond physics, but when he spends his time weaving ponchos and acting like a shut-in, Leonard calls Sheldon's mother for assistance.
Leonard, realizing his pursuit of Penny is fruitless, has an unexpected encounter with a fellow scientist (Sara Gilbert).
Leonard, Sheldon, Wolowitz and Koothrappali attend Penny's Halloween party.
Penny sleeps on Leonard and Sheldon's couch when Wolowitz seduces her friend and takes over her apartment; in need of a fourth member, the guys ask Penny to join their "Halo" team.
On a blind date, Koothrappali discovers that he can talk to the opposite sex after a few drinks, but his date takes an interest in Sheldon.