Episode 1 / The Skank Reflex Analysys

Leonard and Sheldon (series stars JOHNNY GALECKI and JIM PARSONS) are brilliant physicists — wizards in the laboratory, but socially inept outside of it. Enter beautiful, free-spirited neighbor, Penny (series star KALEY CUOCO), who aims to teach them a thing or two about life. While Leonard spends his days looking for love, Sheldon is quite content video-chatting with platonic partner Amy Farrah Fowler (series regular MAYIM BIALIK), or playing Star Trek 3D Chess with their ever-expanding universe of friends, including fellow scientists Raj (series star KUNAL NAYYAR) and Howard (series star SIMON HELBERG), and Howard's fiancée, the adorable micro-biologist, Bernadette (series regular MELISSA RAUCH).

The fifth season premiere picks up where the fourth season finale left off as the gang deals with the aftermath of Penny and Raj's night together. While Penny worries that she's screwed things up permanently with her friends, Sheldon takes command of the paintball team. Emmy® nominee CHRISTINE BARANSKI (The Good Wife) reprises her role as Leonard's emotionally distant mother.

Episode 2 / The Infestation Hypothesis

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 (recurring guest star AARTI MANN), who has moved back to India.

Episode 3 / The Pulled Groin Extrapolation

Leonard attends a co-worker's wedding as Amy's date. Meanwhile, Howard tries to convince Bernadette to live with his mom after they get married by suggesting a trial run with the two of them staying with his mom over the weekend.

Episode 4 / The Wiggly Finger Catalyst

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!

Episode 5 / The Russian Rocket Reaction

Sheldon's old nemesis, WIL WHEATON (guest starring as Himself), returns and invites everyone to a housewarming party. Sheldon threatens to "defriend" Leonard if he attends. But when he hears that BRENT SPINER (guest starring as Himself), the actor who played Commander Data, will be there, Sheldon decides to go to the party after all… only to discover new levels of treachery. Meanwhile, Howard gets an out-of-this-world opportunity that Bernadette reacts to strongly.

Episode 6 / The Rhinitis Revelation

Craving a little motherly love, Sheldon competes with the gang for his mother's attention when she comes to visit. LAURIE METCALF reprises her role as Sheldon's mother, Mary.Craving a little motherly love, Sheldon competes with the gang for his mother's attention when she comes to visit. LAURIE METCALF reprises her role as Sheldon's mother, Mary.

Episode 7 / The Good Guy Fluctuation

A cute comic book artist (guest star COURTNEY FORD) puts Leonard's relationship with Priya to the test; while Sheldon, getting into the spirit of Halloween, tries to scare the guys.

Episode 8 / The Isolation Permutation

Amy is heartbroken when Bernadette and Penny go shopping for wedding dresses without her.

Episode 9 / The Ornithophobia Diffusion

Can friends with benefits still be friends without? Leonard and Penny try hanging out alone, while Sheldon must overcome his fear of birds.

Episode 10 / The Flaming Spittoon Acquisition

Sheldon becomes jealous and considers taking his relationship with Amy to the next level when Stuart (guest star KEVIN SUSSMAN) from the comic book store asks her out on a date.

Episode 11 / The Speckerman Recurrence

Leonard must face his fears after being contacted by his high school tormentor (guest star LANCE BARBER), while Penny realizes that she might have been a bully herself.

Episode 12 / The Recombination Hypothesis

The possibility of Leonard and Penny getting back together could prove disastrous when Leonard offers Penny a spur of the moment invitation to a romantic dinner for two on the 100th episode of the series.

Episode 13 / The Shiny Trinket Maneuver

Sheldon gets in trouble with Amy when he isn't impressed by her recent accomplishment, and it's up to Penny to teach him how to be a better boyfriend. Howard, meanwhile, must come to grips with Bernadette's dislike of children.

Episode 14 / The Beta Test Initiation

Leonard and Penny experiment with dating again by "beta testing" their relationship, while Raj develops a peculiar relationship with his phone's virtual assistant.

Episode 15 / The Friendship Contraction

Sheldon's selfish demands force Leonard to reconsider their friendship. Could this be the end of The Roommate Agreement? Meanwhile, Howard tries to pick his astronaut nickname, but NASA astronaut MIKE MASSIMINO (guest starring as himself) has other ideas.

Episode 16 / The Vacation Solution

When Sheldon is forced to take a vacation by the university, he goes to work with Amy in her neurobiology lab. Meanwhile, Bernadette wants Howard to sign a pre-nuptial agreement.

Episode 17 / The Rothman Disintegration

When a corner office at the University opens up, Sheldon must compete for it with his office nemesis, Barry Kripke. Meanwhile, Bernadette wants Howard to sign a pre-nuptial agreement.

Episode 18 / The Werewolf Transformation

Sheldon's life is turned upside-down after his barber becomes hospitalized. Now, that there's been a change in his routine, Sheldon finds himself re-evaluating his entire life. Meanwhile, astronaut training causes Howard to rethink his decision to go into space.

Episode 19 / The Weekend Vortex

It's on… like Alderaan, when the guys plan a weekend Star Wars gaming marathon! But when Sheldon chooses the guys-only weekend over a weekend with Amy to visit her aunt, he is destined to feel the force!

Episode 20 / The Transporter Malfunction

It's a dream come true for Sheldon when he has a close encounter with his hero, Mr. Spock. Legendary sci-fi icon LEONARD NIMOY guest stars, lending his voice to a unique reprisal of his three-time Emmy®-nominated Star Trek role.

Episode 21 / The Hawking Excitation

When Wolowitz gets tow work with world-renowned scientist STEPHEN HAWKING (guest starring as Himself), Sheldon is willing to do anything to meet his hero.

Episode 22 / The Stag Convergence

Howard's wedding plans are in jeopardy after the guys (and Wil Wheaton) throw him a bachelor party. After details of his sexual history are leaked online, Bernadette reconsiders marrying Howard.

Episode 23 / The Launch Acceleration

When NASA reschedules Howard's mission and puts his wedding plans in jeopardy, he's forced to face his fears and Bernadette's dad (guest star CASEY SANDER). Meanwhile, Leonard says something surprising to Penny in the bedroom.

Episode 24 / The Countdown Reflection

Howard Wolowitz crosses over into the final frontiers of space… and marriage on the fifth season finale. When Howard and Bernadette decide they want to be married before his NASA space launch, the gang rushes to put on a wedding. NASA Astronaut Mike Massimino guest stars as Himself.