Raj faces his loneliness when his friends are out on dates; while in space, Wolowitz gets drawn into a fight between Bernadette and his mom.
Sheldon tries to intervene when he learns that Penny is thinking about breaking up with Leonard; Howard is picked on.
Amy feels threatened by Sheldon's new assistant; Wolowitz starts to feel the pressures of being in space.
Wolowitz's return from space isn't all he expected; game night becomes a gender war.
The gang heads to Stuart's comic book store to celebrate Halloween; Leonard uses science to seduce Penny.
A game threatens Sheldon's relationship with Stephen Hawking; Penny secretly signs up for a college class.
Bernadette wants Wolowitz to move out of his mom's house; Sheldon is caught in the middle of Amy and Wil Wheaton's argument.
Raj and Howard try to figure out why Sheldon disappears at 2:45 every afternoon; jealousy arises in Penny and Leonard's relationship.
Sheldon and Wolowitz's fight over a parking spot at the university impacts the whole gang.
When Amy gets sick, Sheldon tries to nurse her back to health; Wolowitz and his father-in-law plan a fishing trip.
During a game, Sheldon revisits Christmas memories; Amy, Penny and Bernadette look for a date for Koothrappali.
When Sheldon is accused of sexual harassment, he ends up getting Raj, Leonard and Wolowitz in trouble.
As the guys don costumes and go on a road trip to a comic book convention, the ladies decide to stay home and try to interpret a comic book.
Sheldon faces a crisis of confidence when he is forced to work with his nemesis, Barry Kripke; Raj and Howard buy expensive action figures of themselves.
A fight between Sheldon and Leonard impacts Amy and Penny's living arrangements; while Howard is away, Raj helps Mrs. Wolowitz out.
The guys search for a perfect Valentine's Day gift for their significant others; Stuart and Raj host a "lonely people" party at the comic book store.
After a bad date, Koothrappali decides to never leave his apartment; Penny's acting skills impress Sheldon.
Leonard, Sheldon and Wolowitz talk to junior high girls about science-related careers; Raj plans a date with Lucy.
Howard considers whether or not he should open a letter from his father; Penny and Leonard host a "grown-up" cocktail party.
The girls get involved when Leonard, Sheldon and Raj compete for tenure at the University.
Amy tries to help Sheldon get over his compulsive need for closure when one of his favorite TV shows is canceled; Raj discovers a secret about Lucy.
Leonard and Sheldon hire the host (Bob Newhart) of their favorite childhood TV show to perform; Bernadette and Howard run into trouble while dog-sitting for Raj's pet.
Amy and Sheldon's relationship takes a surprising turn during a game of "Dungeons & Dragons"; Lucy and Koothrappali have an awkward date.