The Big Bang Theory

Amy and Leonard take a surprise road trip to Arizona, while Penny goes on a job interview at Bernadette's company, and Howard has problems wrapping his head around Stuart's relationship with Mrs. Wolowitz.

Sheldon is ordered to teach a class, and the gang is surprised when Howard signs up to take it, and tensions between Penny and Bernadette afford Amy an opportunity to play one against the other.

A nervous Wolowitz is thrown for a loop when NASA asks him to toss out the first pitch at a Los Angeles Angels baseball game. Meanwhile, Sheldon brags that he and Amy are a better couple than Leonard and Penny.

Raj's girlfriend, Emily, gives Penny the cold shoulder after he reveals some info about their past history; and the guys contemplate buying into Stuart's comic-book emporium.

Amy and Bernadette accuse former party girl Penny of becoming a party pooper when she lets an email from work impact their girls' weekend in Las Vegas. Meanwhile, the guys brainstorm about inventing something cool.

Sheldon and Raj undertake an underground research expedition that turns into a test of how long before they get under each other's skin. Meanwhile, Leonard and Penny argue about money.

Penny's flirtatious sales pitch leaves a doctor-client smitten and the guys must pitch in to help her deal with him, while Bernadette and Amy debate whether female scientists ought to play the sexuality card.

Amy and Bernadette organize a prom to be held atop the guys' apartment complex but Sheldon is leery of all the prom pomp, circumstance and romancing that goes with it.

Leonard needs surgery for a deviated septum, and Sheldon gets his nose out of joint because he feels an operation is too dangerous and that his roommate may not make it out alive.

It's a banner day for Sheldon as he bids a sad farewell to his Fun With Flags podcast. Meanwhile, Leonard, Howard and Raj probe a late professor's research in search of some hidden significance.

On Christmas Eve, Amy plans a traditional Victorian dinner, while Raj, Leonard and Howard scramble to remove a pigeon that flew into the clean room at the university.

While Raj eagerly awaits data from a space probe in which he was involved, Howard keeps distracting him. Later, dress shopping with Penny and Amy doesn't exactly prove to be a good fit for Leonard and Sheldon.

Sheldon becomes concerned that his cushy lifestyle is impacting his professional progress and keeping him from achieving scientific renown, so he asks the gang to make life more difficult for him.

An online troll rips Leonard and Sheldon's published physics paper, so the guys rally to defend the two and expose the bully, while a girls night out leads to Penny, Amy and Bernadette dishing about embarrassing past events.

Amid the excitement of Stuart reopening his comic-book store, Howard gets some unsettling news; and after teaching Sheldon how to "let it go," Penny doesn't practice what she preaches when she learns something maddening about Amy.

An experiment designed to make participants fall in love piques Penny and Leonard's interest, so they decide to put it to the test. Meanwhile, Leonard, Amy, Raj and Emily have an encounter with a "zombie."

There's trouble in paradise when Amy discovers Sheldon signed up for a one-way mission to colonize Mars, and the two get into a dogfight at a pet store. Meanwhile, Leonard makes a very "adult" purchase for Penny.

An electrical short thaws the last meal that was cooked by Mrs. Wolowitz, and the gang ponders what to do with it, while Sheldon and Leonard's work is featured in a magazine, but only one receives credit.

A speaking engagement at UC Berkeley puts Leonard and Sheldon in a galaxy not too far, far away from their idol George Lucas' Skywalker Ranch, and they considrer dropping by.

When Sheldon and Amy build a fort, they come to a crossroad in their relationship. Wolowitz is shocked when a man claiming to be his half-brother shows up. When Penny is invited to be on Wil's podcast, she and Leonard have an argument.

In the event of alien contact, NASA asks Raj to craft a message for the extraterrestrials, and the guys battle over how it should be handled. Meanwhile, Penny must decide between auditioning for a film role or keeping her job in pharmaceutical sales.

Wolowitz questions his abilities when he and Sheldon can't get a drone to fly. A canceled flight nearly prevents Leonard from giving the commencement address. Raj pits his parents against each other when his father cuts him off financially.

Leonard and Sheldon's mothers come to town to celebrate their sons getting an award, but the opinionated women engage in an altercation over religion.

In the Season 8 finale, Leonard and Penny are pressured to set a wedding date by Sheldon, whose relationship with Amy has taken an interesting turn.