Alan starts working for Evelyn as Charlie works to fix the relationship between Chelsea and Jake.

Alan ends up playing maid to Judith’s new baby as well as his former mother-in-law. Meanwhile, Jake uses an incriminating photo to blackmail Charlie.

When Chelsea convinces Charlie to let Alan’s new girlfriend, Melissa, move in, the girls end up taking over Charlie’s house.

Charlie must make a difficult decision about his future and with which woman he wants to spend his life: Chelsea or Mia.

Charlie starts to question his relationship with Chelsea when he hears that Mia is back in town. Meanwhile, Judith goes into labor and Charlie, Alan and Herb rush her to…

Alan and Chelsea become best buds, and Charlie decides to take advantage of the situation.

Charlie mourns the loss of his bachelor pad as he reluctantly allows Chelsea to move in. Meanwhile, Alan discovers there is no longer much space left in the house for…

Chelsea is asked by Alan to arrange a blind date between he and her new friend, unaware that her new friend is Rose.

Charlie’s desperate to make sure Chelsea and Evelyn don’t befriend each other following their first meeting.

After Chelsea discovers a nude picture of another woman on Charlie’s cell phone, he blows off steam by going out for a night of drinking with Alan, Herb and his…

Chelsea’s illness gives Charlie a chance to prove he can take care of her, but also yearning to run away from the situation.

Charlie’s admission that he’s in love with Chelsea gets a surprising reaction from her

Charlie has to remove a half-naked woman from his bedroom before Chelsea arrives.

Charlie ends up in couples counseling.

Melissa doesn’t think Alan’s family appreciates him, so she asks him to move in with her and her mom.

Judith is pregnant with a baby girl and Alan is convinced he is the father.

Charlie and Jake fight for the affections of a waitress, while Alan fights sexual tension with his receptionist.

A Christmas visit from his mother has Leonard discovering she’s kept a lot of news from him that she shares with Sheldon and worrying if she’ll approve of his romance…

Penny gets help from Sheldon in order to understand what Leonard’s work is, while Wolowitz develops a jealousy when Leonard starts hanging out with his new girlfriend.

After he’s humiliated on National Public Radio, Sheldon vows to destroy Kripke, while Wolowitz tries not to destroy his new relationship with Bernadette.

With Leonard, Howard and Raj away camping in the desert, an injured Penny has only Sheldon to rely on.

A squabble between Leonard and Penny sees Sheldon playing mediator, though out of his own incovenience from the sitiation rather than altruism.

Sheldon becomes Leonard’s teacher in order to understand football, while an incident with flying a kite threatens Howard and Raj’s friendship.

After overhearing that Wil Wheaton is entering a trading-card competition, Sheldon decides to enter it himself. Meanwhile, Penny sets up one of her friends on a date with Wolowitz.

Raj must find a new job or be sent back to India, but Sheldon has a solution, which leaves Leonard and Penny dealing with Howard as a third wheel.

Howard and Raj visit a Goth nightclub to pick up women while Sheldon attempts to build a better Penny using chocolate-based behavior modification.

Leonard and Penny struggle to recover from an awkward first hookup while Sheldon and Howard stake their best comic books on a bet to determine the species of a cricket.

When Sheldon learns the guys tampered with his expedition data he got from the arctic, he leaves to Texas in disgrace. This results in the guys following him, which threatens…

The guys’ plan to work over the summer at the North Pole makes Penny revaluate her feelings for Leonard.

Penny’s second date with Stuart sees her making a comment that gives Leonard new hope for a relationship with her. Wolowitz realizes there’s a crucial error in a NASA project…

Leonard and Koothrappali escort a heartbroken Wolowitz to Las Vegas, and Sheldon becomes locked out of his apartment and must stay with Penny.

A fellow comic book enthusiast’s hitting on Penny leads to Leonard and Howard going to a bar’s Ladies’ Night.

Penny squares off with a new beautiful female neighbor who may become the building’s “new Penny.”

Penny’s home business turns into a complete nightmare when Sheldon takes over.

Leonard, Sheldon and Wolowitz are ecstatic to learn that a famous science-fiction actress (Summer Glau) is on board the train they are taking to San Francisco.

A paintball game leads to a fight between Sheldon and Penny, and romance for Leslie and Wolowitz.

Leonard and Penny are drawn together after a disastrous visit from Leonard’s mother.

Sheldon’s solution to Penny’s financial difficulty leads to a confrontation between Leonard and Penny’s ex-boyfriend.

Sheldon creates a scientific procedure for making friends.

Penny’s criticism of Wolowitz’s romantic life pushes him into depression and AWOL for a fighting robot battle the rest of guys are depending on him for.