With everyone paired up, Raj is left alone and imposes himself on others. Howard cannot escape the two women in his life, even while on the space station.

Penny confides to Amy and Bernadette that she is unsure about staying with Leonard, and when Sheldon inevitably learns about it, he takes matters into his own hands. Howard gets pranked as the new guy in space.

Sheldon hires a young woman to be his assistant, which initially makes Amy jealous, then later Penny finds cause for concern. On the space station, Howard starts to freak out when he learns his return to Earth will be delayed.

Howard is home, but on his first night back Bernadette gets sick so he decides to visit his friends. His reception is not what he expected. Game Night with Sheldon, Leonard, Penny and Amy takes a competitive turn when the girls take on the guys.

Raj and Stuart throw a Halloween bash at the comic book store. Howard is upset when everyone tires of his stories about life on the space station. Leonard shows Penny his laboratory and is surprised by her reaction.

Penny reveals that she is taking a class at the local community college, but insists it is no big deal. Sheldon plays an Internet game with his idol, Stephen Hawking, then frets when Hawking stops playing.

Bernadette puts her foot down about Howard moving out of his mom's house. Sheldon is perplexed with the enmity between Amy and his friend Wil Wheaton and has no clue how to fix it.

Howard is curious why Sheldon disappears every day at 2:45 and asks Raj to help him discover the secret. Penny's new school partner causes Leonard to be jealous.

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.

When Amy gets sick, Sheldon is required to take care of her and she milks it for all it's worth. Bernadette arranges for Howard and her father to bond via a fishing trip.

Leonard leads the boys on a Christmasy version of Dungeons and Dragons, while Raj joins the girls on their night out and they try to find him a girl.

Sheldon manages to put his foot in his mouth and ends up being accused of sexual harassment. In typical fashion, he throws his friends under the bus too.

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.

After being forced to team up with Barry Kripe by management, Sheldon is dismayed when he discovers his work is not up to par with Kripke's. Howard and Raj spare no expense to get action figures that look like themselves.

Leonard finally has enough of Sheldon and moves out, to Penny's distress. Amy takes advantage of Sheldon's need for a new roommate, to Sheldon's distress. While Howard is away, Raj agrees to look in on Mrs. Wolowitz, to his distress!

The three couples celebrate Valentine's day in their own way, with little success while Raj and Stuart throw a party for their unattached friends.

When Raz gets dumped again, he decides to never leave his apartment or have anything to do with girls again. Penny uses her acting skills to help Sheldon with his Fun With Flags videos.

While Leonard, Sheldon, and Howard try to motivate middle school girls to pursue a career in science, the ladies play hooky and go to Disneyland. Raj has a first date with Lucy.

Howard and Bernadette trick Sheldon into organizing their closet where he finds an unopened letter from Howard's father. Howard then struggles whether or not to read it.

A tenured position becomes available at the University and Leonard, Sheldon and Raj all decide to apply, each with their own unique style of currying favor.

Raj's curiosity about his new love interest leads him to discover something to make him change the impression he makes on people. Meanwhile Penny worries that she lacks passion about anything and Amy tries to cure Sheldon of his completion compulsion.

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.

The girls join the boys in a game of Dungeons & Dragons after their trip to Las Vegas falls through. Raj and Lucy continue their dating adventures and Raj pushes Lucy to confront one of her greatest fears.

Leonard gets an opportunity to work with Dr. Stephen Hawking, but the downside is it will mean being away for up to four months. Both Penny and Sheldon are affected tremendously and both try to come to terms with their feelings while still supporting Leonard. Raj risks everything with Lucy when he pushes her too hard and too fast.