Sheldon makes a major scientific breakthrough, but he feels it may haunt him for the rest of career. Meanwhile, Howard makes a grand romantic gesture to Bernadette, which causes Penny to put more effort into her relationship with Leonard.
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When Sheldon's childhood hero, Professor Proton, seeks Leonard's help with an experiment, the slighted Sheldon goes nuclear and decides to get revenge by befriending another TV science guy.
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Leonard fails to stop Sheldon from overreacting after a past slight comes to light, and as punishment Leonard must walk a mile in Sheldon's shoes. Meanwhile, Penny has a run-in with Raj's former girlfriend Lucy.
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When Sheldon's accidental scientific discovery is disproved, Amy and Leonard try to help him deal with the shame and the disappointment. Meanwhile, Howard and Bernadette open their home to Raj for a week.
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With Sheldon in Texas, the gang gathers to decorate for Christmas, and they contemplate if each would have had a wonderful life had they never met him.
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Penny turns to Leonard for comfort after her guest appearance on NCIS does not turn out well. She ends up putting Leonard on the spot regarding their relationship. Sheldon works on his sense of humor and Raj practices talking to girls.
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There's impactful news on the work front as Penny makes a big step toward pursuing a full-time acting career, and Sheldon is forced to take a vacation.
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Amy has amour on her mind when she talks Sheldon into a romantic Valentine's Day getaway to Napa Valley wine country. Back at home, Leonard and Penny make an emergency visit to the vet with Raj's dog.
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Leonard's purchase of a dining-room table for the apartment doesn't sit well with Sheldon, so much so that it forces him to reevaluate his life. Meanwhile, Bernadette isn't quite over the moon about Howard taking another trip to space.
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Things turn rocky between Sheldon and Wolowitz after a barrage of insults, and Bernadette steps in to mediate a peace. Meanwhile, Penny is offered a movie role that may prove embarrassing.
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While Sheldon and Howard continue their bonding, Sheldon's visit to see his mommy forces him to start addressing a new reality. The gang are subjected to a murder mystery party that leads them to speculate where they might be in 20 years.
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Raj wrestles with dating two women at the same time; Penny is offered a part in a trashy movie; and Sheldon can't decide between two gaming systems.
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About
Leonard and Sheldon are brilliant physicists, the kind of ''beautiful minds'' that understand how the universe works. But none of that genius helps them interact with people, especially women. All this begins to change when a free-spirited beauty named Penny moves in next door.
