Creator/producers Chuck Lorre and Bill Prady make comedy a science with the second big season of THE BIG BANG THEORY that makes room for new series regular Sara Gilbert. Check out the physics of funny!
After Penny and Leonard's great date, Leonard tries to kiss Penny in the hallway and realizes that the guys have secretly rigged cameras to spy on them. Penny then tells him that they should take things slow. We find out later when Penny confides in Sheldon that she is actually insecure about not being smart enough for Leonard. She asks Leonard to keep this a secret -- but he is terrible at keeping secrets. After some warm milk laced with valium, he spills the beans to Leonard. Leonard tries to convince Penny that it is not a big deal, but it backfires, and Penny does not want to see him anymore.
Leonard and Penny are no longer dating. Leslie Winkle, played by Sarah Gilbert, moves in on Leonard and proposes to revisit their relationship. Leonard kicks Sheldon out of their apartment so he and Leslie can be on their date alone. Sheldon, who hates Leslie, continually interrupts their date. Sheldon asks Penny for advice on how to break up Leonard and Leslie. He even suggests that Penny get back together with Leonard. Penny comes back with her date and sees Leonard and Leslie. Both Penny and Leonard try to make each other jealous by making out with their respective partners. In the end, Leslie breaks up with Leonard because he supports Sheldon's String Theory over Leslie's Loop Quantum Gravity.
Penny feels frustrated by her failure at everything in her life. She becomes obsessed with playing an online game called "The Age of Conan," and Sheldon tries to help with her addiction by giving her tips on how to get to the next level. She calls him at work for help. When she crosses the boundary by going into Sheldon's room in the middle of the night, he's had enough. Leonard tries to get through to her but fails. Sheldon sets up an online dating profile for her and brings home a guy for her to meet that's supposed to be her perfect match. Penny is so far into the game that she doesn't even notice. Only when Wolowitz propositions her does she snap out of it.
Koothrappali is being honored by People Magazine's "30 under 30" for his discovery of a new planet. The guys all try to express their support and happiness for him except for Sheldon who can't understand why he's being honored for discovering something that already exists. As Raj gets cockier and cockier about it, Leonard and Wolowitz have a harder time being supportive and try to avoid him. Raj invites them all to a party the magazine is throwing for the honorees but they all decline coming. He invites Penny as his date and she accepts. He ends up getting really drunk in order to hang out with her.
Leonard needs to work nights, leaving Sheldon without a ride to or from work. He asks Penny, then Wolowitz, then Koothrappali, but one way or another, he manages to annoy them to the point they won't drive him. Their answer is to stage an intervention -- convincing Sheldon to get his driver's license. The first hurdle is the learner's permit test; Sheldon thinks the questions are poorly phrased, and the DMV clerk is so annoyed with him, she hands him a permit. Since no one is willing to drive with him, they set up a simulator so he can practice driving. It's a disaster and clearly Sheldon isn't cut out to drive.
After speaking at a student seminar, Sheldon finds himself with a groupie named Ramona Nowitzki. She’s young and beautiful and prepared to do anything for Sheldon so he can focus entirely on his work. Leonard, Penny, Wolowitz and Koothrappali are stymied by Ramona’s attentions, especially when they seem to cross professional boundaries. As they try to figure out what Sheldon’s “deal” is, Sheldon appears to be initially charmed by the attention. However, when it gets to be too much, Sheldon has no idea how to extricate himself from the situation.
Penny is now a member of Leonard and Sheldon's group, so she must obey the house rules. After her third strike, Sheldon banishes her. Leonard gets frustrated with Sheldon about this because he and Penny are in a good friendly place with their relationship, but Sheldon is adamant. Leonard goes to Penny and asks her to apologize to Sheldon in order to make peace. She tells Leonard he’s enabling Sheldon and she won’t participate in that. Unfortunately this leads to a war between Sheldon and Penny with things escalating to the point where Sheldon steals Penny’s laundry. Finally, Leonard goes to Penny and gives her Sheldon’s kryptonite -– his mother’s phone number. She uses it, Sheldon apologizes and all is well. Also, Wolowitz learns about the show America’s Next Top Model and becomes obsessed with finding America’s Next Top Model house.
Leonard, Sheldon and Koothrappali are using Rock-Paper-Scissors-Lizard-Spock to decide what to watch on TV when they're interrupted by a phone call from Wolowitz. Wolowitz has picked up a woman, Stephanie, by telling her he can let her drive the Mars Rover; unfortunately, he drives it into a ditch and needs help. Leonard escorts Stephanie home, while Sheldon and Koothrappali help Wolowicz. Leonard and Stephanie end up making out in the car and start dating. Wolowitz is furious until they invite him on a double date with Stephanie's roommate.
Leonard continues to date Stephanie and things seem to be going well as far as he's concerned. Sheldon, however, is worried that Leonard isn't handling things correctly; Sheldon really likes Stephanie and it's extremely important to him that Leonard's relationship go well. At first he seeks Penny's perspective on Leonard's relationship deficiencies, then orchestrates things to make Leonard seem more manly. When this backfires, he decides to hack Leonard's Facebook page, and change Leonard's relationship status to "in a relationship." Leonard's furious that Sheldon has forced him into the cyber-equivalent of saying "I love you" first, but when Stephanie reciprocates, all ends well.
Penny councils Leonard about his relationship with Stephanie when he realizes that the only reason he is dating her is that she likes him. He tries to break it off, but each time he tries they end up having sex. Finally he breaks up with her by text message.
Leonard meets his intellectual superior in award winning scientist David Underhill. Underhill is the total opposite of Leonard: handsome, charming, and cool. He's the whole package of brains and looks which initially doesn't sit well with Leonard. Although when Hill asks for Leornard's help in research he is undertaking, he happily jumps at the offer. Leonard's joy of working with Hill is hampered by jealousy when Underhill takes an interest in Penny and the feelings are reciprocated.
Sheldon, having always viewed the holidays as a pagan ritual that is rooted in obligations rather than holiday cheer, is taken for a loop when Penny brings him a Christmas gift. He now feels obligated to buy her a gift and enlists Wolowitz and Koothrappali to help him with this task which they reluctantly agree to. Sheldon believes he has come up with the most logical gift giving scenario until he opens Penny's gift; he cannot believe what she got him.
The guys are excited about building a “killer” robot named Monte for a regional robot fighting league when Kripke challenges them to a robot duel which Sheldon jumps at. The duel goes awry and Monte is the causality. Penny finally tells Wolowitz what she thinks of his crude behavior toward women and he is devastated by her comments; Leonard convinces her to go apologize. Just as she starts to sympathize, Wolowitz once again misreads the signs and Penny has a violent reaction.
Sheldon needs to use a new super computer that has just arrived at the University but when Leonard informs him that Kripke controls who can use the computer and he only allows his friends to use it, Sheldon makes it his mission to befriend Kripke. The guys are skepitical if Sheldon can do it since they point out that he has never made any effort to befriend anyone in his life; not even them. Sheldon surmises that he must take a scientific approach to friendship. He figures out, what he feels, is a fool proof "friendship" algorithm. Kripke agrees to meet with Sheldon and things seem to be going well until Sheldon asks Kripke to use the computer. Kripke turns Sheldon down and Sheldon inquires as to why since they are now friends. Kripke informs him that he has no control over who uses the computer and all Sheldon has to do is sign up for the official schedule. Sheldon realizes all this research was for nothing and immediately dumps Kripke as a friend.
When Penny runs into financial trouble, Sheldon gladly offers to lend her money. Penny is uncomfortable with taking money from him and begins to act out her frustration which confuses Sheldon entirely. Leonard soon finds out that her financial troubles began when she lent money to her ex-boyfriend, Kurt, who has never paid her back. Without Penny's knowledge, Leonard then decides to get the guys together to confront Kurt and get her money back. It doesn't go exactly as Leonard plans but soon enough Penny's ex shows up at her door and returns the money. Penny is so taken by Kurt's gesture that she believes he has changed his ways and agrees to go out on a date with him to Leonard’s dismay.
Leonard’s mother (played by Christine Baranski), a brilliant neuroscientist who has no concept of appropriate human interaction or warmth, comes for a visit. During her stay, she manages to alienate and cause emotional turmoil in everyone’s lives except for Sheldon who is taken by her since they are so much alike. Leonard is not in the least happy with her presence and Penny feels likewise after his mother makes Penny explore and question her relationship with her father; both Penny and Leonard turn to each other and a bottle of tequila for comfort which leads them to explore much more than their individual childhood issues.
Wolowitz begins to date Leslie (played by Sara Gilbert) with Leonard’s blessing. Leslie has access to unrestricted grant money that she is using towards Wolowitz's research while the other guys are having their budgets cut. Wolowitz soon realizes that Leslie intends to have a relationship of convenience with no real feelings involved and Wolowitz questions if he is okay with the idea of being used as a sex object; but only for a minute. Meanwhile, Penny accidentally ruins Sheldon’s “spot” on the couch; Sheldon’s neurosis hits a new level when he tries out different areas in the apartment to find a new spot with no success.
The guys are going to attend a symposium featuring Dr. George Smoot (Nobel Laureate for his work on the Big Bang) in San Francisco. Sheldon decides for the group that the train is the best way to travel and while initially the other three were not thrilled, their mood soon changes when they realize Summer Glau, "The Terminator", is on the train with them. Koothrappali, Wolowitz and Leonard argue about who will hit on her first. Koothrappli decides he should get some alcohol in him since he knows he is unable to hit on women sober. As Wolowitz is about to make his move, Koothrappali swoops in and in his seemingly drunken state, charms Summer to Wolowitz's dismay.
Sheldon forgets his flash drive at home which contains a research paper he planned to present to Dr. Smoot at the symposium. He initially wants to turn back to get the flash drive but Leonard convinces him to call Penny since she has the key to their apartment. Sheldon reluctantly agrees and allows Penny access to one place no woman has ever been; his bedroom.
Sheldon helps Penny start her own business making hair clips. Leonard and the rest of the guys pitch in to start a website and manufacture her goods. The website is pretty lame -- and they are tease Leonard about it. In the mean time Sheldon has his first cup of coffee and he is bouncing off the walls. The gang has to make 1000 Penny Blossoms over night for an order that ships the very next day.
Penny has become one of the guys around our guys. She dresses in sweats -- hair in a pony tail -- and she is not at all prepared when a new, very hot girl moves into the building. Leonard, Koothrapali and Wolowitz go crazy for this girl. They do everything for her, and it drives Penny crazy. She tries to compete with this girl, but she is just the new flavor - and they pay no attention to Penny. The episode culminates with the new girl getting a part on CSI -- and when she doesn't need the guys anymore, she dumps them. This episode ends with penny and the new girl getting in a knock down, drag out CHICK FIGHT!
In this episode Penny is hit on by the sales clerk in a comic book store that the guys frequent. Leonard is devastated at this turn of events. He can't believe that Penny would date one of "them" if it isn't him. In the mean time, Sheldon gets in the middle of the budding romance by constantly challenging the new guy to engage in a Batman dialogue. The new guy is such a nerd, that he falls right into Sheldon's hands. Penny ends up asleep on the couch while the guys hash it out over what Robin's real name is.
When Wolowitz is dumped by Leslie Winkle, the guys take him to Vegas. He hides in his room the whole time looking at Leslie's Facebook page. The guys finally lure him out with a prostitute. In the mean time, Sheldon stays back home and gets locked out of his apartment. He ends up spending the night at Penny's place.
Stuart, played by Kevin Sussman, the comic book sales clerk goes to Leonard to ask his advice on dating Penny. Leonard advises him to act very shy around Penny. Leonard later finds out that Stuart's date with Penny goes all wrong because while making out, Penny calls out Leonard's name. In the mean time, Wolowitz has designed a toilet for the International Space Station, and has left out one of the most important parts. All the guys rally around to try to find a fix for the space toilet.
Sheldon is approached by the Dean of the University to lead a scientific expedition to the Arctic. He invites the guys to go along with him for the summer and be his team. After much banter about how difficult it would be to spend a whole summer in such tight quarters with Sheldon, they decide it is too good of a career opportunity to pass up. When Penny hears the news, she knits a cap and scarf for Leonard. He is not sure how to take this, as he still has feelings for her and wonders if this may mean that she has unspoken feelings for him. He decides to ask her what the meaning was behind the gift, and she tells him she will miss him. He questions if that is all that she wants to say. Although she is tentative in her response, it is clear that they have a special connection. The show and season end with all of the guys, including Leonard, in a hut in the Arctic.