The Big Bang Theory

Leonard and Amy take an unexpected road trip to Arizona to pick up Sheldon. Meanwhile, Penny interviews for a job at Bernadette's company.

When Sheldon (JIM PARSONS) is forced to teach a class, Howard (SIMON HELBERG) surprises everyone by taking it. Guest star REGINA KING returns as Mrs. Davis.

Howard's nervous when NASA asks him to throw out the first pitch at a game. Also, Leonard & Penny try to prove Sheldon wrong after he claims that he & Amy are a superior couple.

Raj's honesty about his past comes back to bite him after his girlfriend, is cold to Penny. Meanwhile, the guys consider becoming part-owners in Stuart's comic-book store.

With the girls away in Vegas for the weekend, the guys try to invent "the next big thing," but only come up with new ways to procrastinate.

Sheldon and Raj see if they can survive intense heat - and each other - when they venture deep underground in the name of science.

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.

When the gang recreates a high-school prom night on the roof of the guys' apartment building, Sheldon feels pressure to participate in all the typical romantic traditions.

When Leonard gets minor surgery on his nose, Sheldon has a major overreaction. Meanwhile Howard and Bernadette work on their marriage in light of Raj's parents' impending divorce.

As Sheldon records the final installment of "Fun with Flags," Bernadette is shocked to learn of her co-workers' true feelings from Penny.

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.

When the guys finally agree to do something the girls like, it leads to a confrontation between Leonard and Sheldon.

Sheldon worries his comfortable lifestyle is preventing him from achieving scientific progress so he asks his friends to make him miserable.

When an online bully destroys Leonard and Sheldon's physics paper, the guys band together to take him down.

Howard receives some shocking news as everyone prepares for the reopening of Stuart's comic book store, and Penny teaches Sheldon how to "let it go."

When the gang hears about an experiment designed to make participants fall in love, Sheldon and Penny put it to the test as a joke.

Trouble arises when Amy learns that Sheldon has applied for a one-way mission to colonize Mars.

When a magazine incorrectly credits Sheldon as the lead scientist of the paper he co-wrote with Sheldon, things get awkward.

When Leonard and Sheldon are invited to speak at UC Berkeley, they take a detour to try to sneak on to George Lucas's Skywalker Ranch to meet their idol.

Wolowitz is shocked when a man claiming to be his half brother shows up at the front door; and Sheldon & Amy reach a crossroads in their relationship while building a blanket fort.

Penny contemplates a return to acting, while Raj is tasked with creating a message for NASA in case a mission discovers alien life — prompting a fight with the guys.

Raj faces a threat to his easy lifestyle when he is cut off from the family fortune, while a canceled flight nearly prevents Leonard from speaking at his former high school.

Sheldon & Leonard's mothers finally meet. Meanwhile, Howard decides to "man up" and do his fair share of the housework -- with a little help from his friends.

In the eighth season finale, Sheldon presses Leonard and Penny to choose a date for their wedding, while dealing with dramatic changes in his own relationship with Amy.