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.
Sheldon once again has to keep a secret when he learns Leonard and Penny are going to break up. Howard keeps getting teased by his fellow astronauts in space.
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.
The University decides to reassign Sheldon's unused parking space to the newly popular Howard, a move that Sheldon feels is a slap in the face to his importance. This starts a feud between the two friends that spills over to their ladies, and Penny pays the price.
Sheldon tries to nurse a sick Amy back to health, while Wolowitz prepares for an upcoming fishing trip with his father-in-law.
Guys plan to play Dungeons and Dragons, but girls are not invited, which causes arguments among them and the girls. After playing for some time at the apartment, the girls show up dressed sexily for a girls' night out and Raj goes with them to the nightclub. After striking out with a woman at the bar, Amy and Raj get to know each other better.
Sheldon gets accused of sexual harassment at the University and winds up getting Leonard, Raj and Wolowitz in trouble.
The guys head out to a comic book convention and get stranded in full costume. The girls decide to try to understand their men and end up in a heated debate over a comic book character.
Sheldon is forced to work with Barry Kripke and faces a crisis of confidence. Meanwhile, Howard and Raj spend ,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.
Leonard tries to get Penny as excited about Buffy the Vampire Slayer as he is. Amy tries to get Sheldon to stop having to finish things by starting various things and not letting him finish them. Raj finds Lucy's blog mentioning that he is somewhat feminine.
Sheldon learns that his childhood television idol, Professor Proton, is still alive and hiring himself out for parties, so of course Sheldon hires him to perform. Raj is away for the weekend so he asks Howard and Bernadette to look after his dog, with the expected result.
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.
A new success for Leonard makes Sheldon very jealous and throws Penny for a loop. Meanwhile, Koothrappali pushes Lucy too far in their relationship.