Everything might change when Leonard offers Penny a spur of the moment invitation to a romantic dinner for two on the 100th episode of the series.
Sheldon gets in trouble with Amy, and it's up to Penny to teach him how to be a better boyfriend. Howard, meanwhile, must come togrips with Bernadette's dislike of children.
Leonard must face his fears after being contacted by his high school tormentor (guest star LANCE BARBER), while Penny realizes thatshe might have been a bully herself.
Sheldon becomes jealous and considers taking his relationship with Amy to the next level when Stuart (guest star KEVIN SUSSMAN) fromthe comic book store asks her out on a date.
Can friends with benefits still be friends without? Leonard and Penny try hanging out alone, while Sheldon must overcome his fearof birds.
Amy is heartbroken when Bernadette and Penny go shopping for wedding dresses without her.
A cute comic book artist (guest star COURTNEY FORD) puts Leonard's relationship with Priya to the test; while Sheldon, getting intothe spirit of Halloween, tries to scare the guys.
Craving a little motherly love, Sheldon competes with the gang for his mother's attention when she comes to visit. LAURIE METCALFreprises her role as Sheldon's mother, Mary.
Sheldon and Leonard get invited to a housewarming party at WIL WHEATON's house; while Howard gets an out-of-this-world opportunity!
When Raj is upset he's the only one of the four guys who is not in a relationship, Penny sets out to find the perfect date,introducing him to Emily (guest star KATIE LeCLERC - Switched at Birth) a girl he can actually talk to!
Attending a co-worker's wedding, Leonard and Amy (MAYIM BIALIK) get to know each other better, while Howard and Bernadette spend the weekend with Mrs. Wolowitz!
A battle of wills between Sheldon and Penny leaves Amy caught in the middle, while Leonard tries to spice up his long-distance relationship with Priya (AARTI MANN).
On the fifth season premiere, Penny worries that she's screwed things up permanently with her friends after her night with Raj,while Sheldon takes command of the paintball team.
After hearing Leonard and Priya indulge in a Star Trek bedroom fantasy, Raj moves in with Sheldon on the fourth season finale.
When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.
Raj attempts to cure his social anxiety disorder of talking to women, while Penny uses Bernadette to spy on Leonard and his girlfriend.