With his friends on dates, Raj must face his loneliness. Also, Wolowitz is caught in an argument between Bernadette and his mom, even while he's in space.
When Sheldon learns that Penny is thinking about breaking up with Leonard, he tries to intervene. Meanwhile, in space, the other astronauts pick on Howard.
Amy feels threatened when Sheldon hires a young female assistant, and the pressure of being in space takes its toll on Wolowitz.
When Wolowitz returns from space, he doesn't get the hero's welcome he expected. Meanwhile, Game Night turns into a battle of the sexes.
The gang celebrates Halloween at Stuart's comic book store. Meanwhile, Leonard seduces Penny with science.
Sheldon's relationship with Stephen Hawking is threatened over a game of "Words with Friends," and Penny secretly enrolls in a class at the local college.
Wolowitz struggles with moving out of his mother's house. Meanwhile, Sheldon is caught in the middle of an argument between Amy and Wil Wheaton.
Howard and Raj try to get to the bottom of why Sheldon disappears every afternoon at 2:45. Meanwhile, Leonard and Penny deal with jealousy in their relationship.
When the University reassigns Sheldon's parking spot to Wolowitz, their fight affects the whole gang.
Sheldon tries to nurse a sick Amy back to health, while Wolowitz prepares for an upcoming fishing trip with his father-in-law.
Sheldon revisits some Christmas memories during a game of Dungeons and Dragons, while Penny, Bernadette and Amy try to find a girl for Koothrappali when he joins the girls for ladies' night.
Sheldon gets accused of sexual harassment at the University and winds up getting Leonard, Raj and Wolowitz in trouble.
While the guys take a road trip to a comic book convention dressed as "Star Trek: The Next Generation" characters, the girls stay home and try to interpret a comic book.
Sheldon is forced to work with Barry Kripke and faces a crisis of confidence. Meanwhile, Howard and Raj spend $1,000 on action figures of themselves.
When Sheldon and Leonard fight, it affects Penny and Amy's living arrangements. Meanwhile, Raj takes care of Mrs. Wolowitz while Howard is away.
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.
After a terrible date, Koothrappali vows to never leave his apartment. Meanwhile, Penny actually impresses Sheldon with her acting skills.
Leonard, Sheldon and Wolowitz speak to junior high girls about careers in science. Meanwhile, Koothrappali plans a date with Lucy.
Howard struggles with whether or not he should open a letter from his father, and Leonard and Penny throw a "grown-up" cocktail party at the apartment.
Leonard, Sheldon and Raj fight for tenure at the University, and the competition heats up when the girls get involved.
Sheldon feels lost after one of his favorite TV shows gets canceled too soon and Amy tries to help him get over his compulsive need for closure. Meanwhile, Raj discovers a secret about his new love interest, Lucy.
Sheldon and Leonard hire Professor Proton, the host of their favorite childhood TV show, to perform. Also, Howard and Bernadette run into trouble babysitting Raj's dog.
When the girls' trip to Vegas falls through, the guys invite them to play Dungeons & Dragons, causing Sheldon and Amy's relationship to take an unexpected turn. Meanwhile, Koothrappali and Lucy go on a very awkward date.
New success for Leonard makes Sheldon very jealous and throws Penny for a loop. Meanwhile, Koothrappali pushes Lucy too far in their relationship.