While the guys try to give their significant others the perfect Valentine's Day, Raj and Stuart throw a lonely people party at the comic book store.
A fight between Leonard and Sheldon drives Leonard to finally move in with Penny – not realizing how the shift will affect Penny and Amy's living arrangements. Meanwhile, Raj takes care of Mrs. Wolowitz while Howard is away.
Outraged that he's being forced to work with his university nemesis, Barry Kripke (guest star JOHN ROSS BOWIE), Sheldon faces a crisis of conscience. Meanwhile, Howard and Raj spend a thousand dollars on action figures of themselves.
While the guys take a road trip to a comic book convention in Bakersfield dressed as characters from Star Trek: The Next Generation, Leonard's car is stolen. Meanwhile, the girls stay home and try to appreciate the world of comics.
Sheldon is accused of sexual harassment at the University and winds up dragging Leonard, Raj and Howard into the fray. Southland's REGINA KING guest stars as the University's Director of Employee Relations.
Sheldon unwillingly revisits some Christmas memories during a lively game of Dungeons and Dragons, while Penny, Bernadette and Amy try to find the perfect girl for Raj when he joins the girls for ladies night.
Sheldon plays nursemaid to a sick Amy, while Howard attempts to bond with his father-in-law (guest star CASEY SANDER) on an upcoming fishing trip.
When the University reassigns Sheldon's (unused) parking spot to Howard, the ensuing turf battle affects the whole gang.
Howard and Raj try to get to the bottom of why Sheldon disappears every afternoon at 2:45. Meanwhile, Leonard and Penny wrestle with jealousy in their relationship.
Pressured by Bernadette, Howard comes to terms with moving out of his mother's house. Meanwhile, Sheldon, who's caught in the middle of a feud between his "girlfriend" Amy and good friend WIL WHEATON, goes to Penny for advice. Star Trek's LeVAR BURTON guest stars.
Sheldon's tenuous relationship with renowned scientist STEPHEN HAWKING is threatened by a game of "Words with Friends," while Penny secretly enrolls in a class at the local college.
The gang celebrates Halloween at Stuart's comic book store. Meanwhile Leonard and Penny discover a new spark in their relationship when he seduces her with science. And while Howard can't stop talking about space, it takes iconic astronaut BUZZ ALDRIN (guest starring as himself) to get him grounded again.
When Howard returns from space, he doesn't get the hero's welcome he expected. Meanwhile, Game Night turns into a battle of the sexes.
While the pressures of being in space starts to take its toll on Howard, Amy feels threatened when Sheldon hires a young female assistant, Alex (guest star MARGO HARSHMAN.)
When Sheldon learns that Penny is thinking about breaking up with Leonard, he tries to intervene. But Sheldon is no good at keeping secrets. Meanwhile, Howard is being picked on in space by the other astronauts (guest stars Pasha Lychnikoff and Mike Massimino.)
On the sixth season premiere, Howard discovers that he can't escape his mother – even in space! Caught in an argument between Bernadette and his mom (recurring guest voice CAROL ANN SUSI), Howard deals with woman trouble from the International Space Station. Back on earth, meanwhile, Raj faces his loneliness, by turning his existence as a third wheel into an art form.
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