With Leonard away, Sheldon and Penny spend quality time together sharing intimate secrets. Also, Wolowitz helps Raj get over his ex-girlfriend.

Leonard and Sheldon's friendship is tested; Howard's latest foray into helping his mother has some disastrous side effects.

When the entire gang competes in a scavenger hunt designed by Raj, it brings out the best - and worst - in everyone.

Sheldon gets mad at Amy for ruining one of his favorite movies, Raj and Stuart try to make their online dating profiles more appealing, and Leonard tries to play the sympathy card with Penny.

Amy starts working at Caltech which causes friction with Sheldon. Howard agrees with Sheldon who mentions this to Bernadette causing a big fight for the Wolowitzes.

Sheldon's latest scientific breakthrough leaves him feeling like a fraud; a romantic gesture between Howard and Bernadette causes Penny to up her game with Leonard.

Sheldon seeks payback when Arthur "Professor Proton" Jeffries asks Leonard for help on a project instead of him. Raj gets upset at Howard for crashing his night with the girls.

When a mistake comes to light, Sheldon makes Leonard walk a mile in his shoes; Penny decides to confront Raj's ex-girlfriend, Lucy.

Sheldon protests when the gang drags him to Mrs. Wolowitz’s house for Thanksgiving. Meanwhile, Penny and Leonard must deal with a mistake from her past.

Leonard has to deal with the fallout of disproving Sheldon's new scientific discovery. Raj spends a week at Howard and Bernadette's apartment.

While Sheldon is at home in Texas, the rest of the gang realizes how much he has changed their lives as they decorate the apartment Christmas tree.

When Penny’s big acting break on NCIS is a bust, Leonard struggles to help her, which results in Penny asking Leonard a bold relationship question. Meanwhile, Raj and Stuart try to practice their social skills, and Sheldon navigates the intricacies of being funny.

Sheldon tries to relax after he is forced to take a vacation. Meanwhile, Leonard struggles to be supportive of Penny after she quits her job, and Bernadette seeks Stuart’s help in replacing one of Howard’s comic books. Also, Amy receives an unwanted attention from a co-worker.

After the guys can’t get Comic-Con tickets, Sheldon tries to hold his own convention and winds up spending a wild night with James Earl Jones. Meanwhile, the girls try to feel more mature by going to a fancy hotel for tea.

Sheldon and Amy take a train ride to Napa Valley with Howard and Bernadette on Valentine's Day. Leonard and Penny take Raj's dog to the vet when she accidentally eats some chocolate.

Leonard buys a dining room table and it causes Sheldon to reevaluate the changes in his life. Meanwhile, Wolowitz is offered a chance to go back to space and Bernadette struggles with whether or not to encourage him.

After arguing with Sheldon, Howard tries to make amends by taking him to NASA headquarters in Houston. Penny has second thoughts about quitting her waitressing job when her car dies. Amy gets involved in trying to find Raj a date.

When Sheldon visits his Mom in Houston, he is forced to confront a new reality. Meanwhile, Raj’s ‘Murder Mystery’ party starts some fights within the gang.

While Raj is wracked with guilt when he tries to date two women at once, Penny wrestles with whether to take a role in a cheesy movie and Sheldon is torn trying to choose between two gaming systems.

Sheldon faces a personal crisis after deciding he’s wasting his time with string theory. Meanwhile, a double date between Raj, Emily and the Wolowitzes ends in embarrassment for Howard.

To prepare for a date with Emily, Howard acclimates Raj to horror movies. Penny and Sheldon are upset when they discover Amy and Bernadette lied to avoid hanging out with them.

As the gang celebrates Star Wars Day, Sheldon has difficulty dealing with the recent death of Arthur "Professor Proton" Jeffries.

A bad day causes Penny to reevaluate her life choices – including Leonard. Meanwhile, Howard and Bernadette struggle to care for Mrs. Wolowitz, and Raj gets relationship advice from Sheldon.

Sheldon get upset about his career, the destruction of the comic book store and Leonard and Penny's future living arrangements. Howard and Bernadette can't keep hold of a caretaker for his mother. With his entire world changing around him, Sheldon considers a major move.

Leonard and Amy make an unexpected trip to Arizona to fetch Sheldon; Penny interviews for a job at Bernadette's company; Stuart's relationship with Mrs. Wolowitz disturbs Howard.

Sheldon is forced to teach a class as a Junior Professor and Howard decides to enroll in it. Meanwhile, Amy plays both sides when tension arises 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.

The girls head to Las Vegas for some weekend fun, while the guys try to invent something cool, but only come up with new ways to procrastinate.

Sheldon and Raj test whether they could survive a dark-matter research expedition in a salt mine by simulating the conditions in a steam tunnel deep underground. Meanwhile, Leonard and Penny seek advice from Howard and Bernadette after they fight about money.

The guys try to help Penny out of an awkward work dilemma, when a smitten doctor shows up at her door after her flirtatious sales techniques work a little too well. Meanwhile, Amy and Bernadette argue over whether or not female scientists should play up their sexuality.

The girls decide to re-enact their high school proms with the guys. While Sheldon feels under pressure to commit to his relationship with Amy, Howard worries about who Stuart will bring as his date.

When Leonard gets minor surgery on his nose, Sheldon is the one in need of sympathy. Meanwhile, Raj's parents' impending divorce causes Howard and Bernadette to work on their own marriage.

While Sheldon says a tearful goodbye to the final installment of "Fun with Flags", Leonard, Howard and Raj search for something significant in a dead professor's research. And Bernadette finds out what her colleagues really think of her.

Leonard and Howard turn to Raj for help in dealing with a work emergency when they nearly come to blows after blaming each other for a potential disaster at the university. Amy throws an authentic Victorian Christmas party, while Sheldon seeks revenge on her for making him celebrate the holidays.

Howard tries to distract Raj, who is anxiously awaiting data from a space probe he helped launch. Meanwhile, Sheldon and Leonard go dress shopping with Penny and Amy.

When Sheldon becomes stuck in a rut with his work, the gang tries to help him by raising his stress levels. Howard teases Raj with a game called "Emily or Cinnamon?"

Leonard and Sheldon publish a paper which is widely accepted except for comments from an internet troll. Meanwhile, the girls reminisce about embarrassing incidents from their past.

Howard receives some shocking news as everyone prepares for the reopening of Stuart’s comic book store. Penny teaches Sheldon how to “let it go,” but can’t follow her own advice after she learns something infuriating about Amy. Also, Leonard and Raj think they spot Nathan Fillion at a restaurant.

As a joke, Sheldon and Penny try an experiment designed to make participants fall in love. Meanwhile, Leonard, Amy, Raj and Emily spend the evening trying to escape a room with a “zombie.” And, after returning from Mrs. Wolowitz’ funeral, Bernadette and Howard run into trouble at the airport.

A trip to the pet store ends in a fight after Amy learns Sheldon has applied for a one-way mission to colonize Mars. Meanwhile, Leonard surprises Penny with a very "adult" purchase, and Raj gets into trouble when he snoops around Emily's apartment.

Friction ensues when a magazine fails to mention Leonard in an article about the paper he co-wrote with Sheldon. Also, a blackout at Mrs. Wolowitz’s home leads to a final family dinner in her honor.

When Leonard and Sheldon are invited to speak at UC Berkeley, they take a detour to try to meet an idol. Also, when Bernadette and Howard battle over the fate of his Doctor Who TARDIS, Raj and Amy offer to settle the dispute with a game of ping pong.

When Sheldon and Amy build a blanket fort, they come to major crossroads in their relationship. Also, Howard meets the half-brother he never knew he had. Meanwhile, Penny is invited to appear on Wil Wheaton’s podcast, but things turn awkward when Leonard joins them.

When Raj is asked to create a message in case a NASA mission discovers alien life, the guys fight over what he should do. Also, Penny is torn between auditioning for a movie or keeping her successful pharmaceutical sales job.

Howard questions his engineering abilities when he and Sheldon can’t get a toy drone to fly. Meanwhile, a cancelled flight nearly prevents Leonard from giving the commencement address at his former high school, and Raj pits his parents against each other when his father cuts him off financially.

Personalities collide when Sheldon and Leonard’s mothers finally meet. Meanwhile, Howard finally decides to “man up” and do his fair share of the housework – but not without a little help from his friends.

As Sheldon presses Leonard and Penny to set a wedding date, he encounters major changes in his own relationship with Amy. Meanwhile, Raj contemplates breaking up with Emily, and Howard and Bernadette struggle with asking Stuart to move out of their house.

After driving to Vegas to get married, Penny struggles with Leonard’s confession that he kissed another girl. Also, Sheldon doesn't know how to act after Amy pushes pause on their relationship.

Leonard confronts the woman he kissed on the North Sea in an attempt to set Penny's mind at ease. Also, Sheldon films a special episode of "Fun with Flags" after his breakup with Amy, and Bernadette feels guilty about withholding a secret from Penny.

The guys' science skills are put to the test when they get a flat tire during Leonard's bachelor party weekend in Mexico. Also, the girls force Penny to finally tell her family that she eloped with Leonard.

Sheldon learns of an impending change in his living arrangements and decides to revert back to 2003, a simpler time before he met Leonard and Penny. Also, Howard and Raj form a band to play at the Comic Book Store.

The guys take a fencing lesson from Barry Kripke and Sheldon finds himself in an awkward position when Kripke expresses interest in Amy. Also, when Stuart struggles to get female customers at the Comic Book Store, Penny, Amy and Bernadette come by to help him out.

In the midst of a nation-wide helium shortage, Sheldon and Leonard take desperate measures to get the supplies they need. Also, Penny and Bernadette download a dating app on Amy's phone to try and find her a new man.

Wil Wheaton interviews Sheldon for a Star Trek documentary where he reveals the ring and his plan to propose to Amy. Bernadette wants to start renovating the house and the topic of starting a family together with Howard is brought up.

Sheldon, Wolowitz and Koothrappali post an online advertisement to find Sheldon a new girlfriend. Also, when Amy is coy with details about a guy she is dating, Penny and Bernadette decide to spy on her.

Sheldon and Amy try hanging out as friends when they spend Thanksgiving together at the aquarium. Also, Wolowitz reluctantly agrees to volunteer at the soup kitchen with Bernadette, Raj and Emily, and Penny discovers that Leonard knows more about her than she thought.

Sheldon has a revelation when he realizes why a song was stuck in his head. Also, Amy invites Dave over for dinner despite their previously awkward date, and Wolowitz and Koothrappali become obsessed with a fan of their band, "Footprints on the Moon".

After more than five years of dating, Sheldon and Amy spend their first night together. Also, Leonard, Wolowitz, and Koothrappali must decide who will take their extra Star Wars movie ticket.

Penny gets more than she bargained for when Leonard agrees to meet with a psychiatrist on her behalf. Also, Sheldon and Koothrappali collaborate on an astronomical discovery, and Wolowitz and Bernadette can't believe what they are feeling after Stuart moves out.

After having to deal with a sick Sheldon, Leonard, Penny and the gang try to treat themselves to a Sheldon-free weekend.

Meemaw meets Amy, but it isn't all roses. Meemaw seems to have an axe to grind with her. Sheldon comes to Amy's defense, but not before Meemaw lets a little secret of his slip.

Sheldon and Amy host a live Valentine's Day episode of Fun with Flags, Leonard and Penny grapple with getting older, Howard and Bernadette find a surprise in their hot tub and Raj is torn between Emily and the cute girl he met at the Comic Bookstore.

When the gang finds out about Bernadette’s pregnancy, they celebrate by singing karaoke. Also, Bernadette is concerned when Wolowitz freaks out over her pregnancy announcement, and Wolowitz is convinced he must make more money to provide for the baby.

After more than nine years together, the gang finally celebrates Sheldon’s birthday, surprising him with a special guest.

Leonard, Sheldon, and Wolowitz run into problems when they file for a patent for their infinite persistence gyroscope. Also, Penny, Amy and Bernadette give Koothrappali dating advice when Emily reaches out to him after their breakup.

Amy is shocked at a revelation from Sheldon after she buys him a new laptop. Also, Koothrappali sells out Leonard and Wolowitz after they lie to their wives in order to attend an early screening of a movie.

Sheldon spills a secret of Leonard’s when the two take a weekend cabin trip with Penny and Amy. Also, when Koothrappali goes overboard with pregnancy gifts, Wolowitz and Bernadette must draw the line.

Everyone must choose sides when a small argument between Leonard and Sheldon erupts into a heated fight during a group get-together.

The gang goes to a wine bar and runs into Penny’s old boyfriend, Zack. Also, Bernadette gets stuck spending the evening with Sheldon when she can’t go wine tasting with the group, and things don’t go as planned when Koothrappali introduces his new girlfriend, Claire.

Sheldon hires Stuart to spend the day with Amy when he’d rather go to a movie screening. Also, Leonard’s mother, Beverly, comes to town and Penny struggles to make a connection with her.

Chaos ensues when Leonard’s recently divorced parents, Alfred and Beverly, and Sheldon’s devoutly religious mother, Mary, come to town. Also, Wolowitz and Koothrappali think the government is out to get them when they are contacted about their guidance system.