Worlds collide in Season 3! A love affair with Penny has opened a big, wide, wonderful world of romance for Leonard. But Sheldon likes the world just the way it was, thank you. All of which makes for a zany comic triangle with brainy, clueless Sheldon and practical, grounded Penny hilariously vying for the role of hypotenuse.
When Sheldon learns the guys tampered with his expedition data he got from the arctic, he leaves to Texas in disgrace. This results in the guys following him, which threatens Leonard's hope for some romantic time with Penny and the guys' friendship with Sheldon.
Leonard and Penny struggle to recover from an awkward first hookup while Sheldon and Howard stake their best comic books on a bet to determine the species of a cricket.
After overhearing that Wil Wheaton is entering a trading-card competition, Sheldon decides to enter it himself. Meanwhile, Penny sets up one of her friends on a date with Wolowitz.
After he's humiliated on National Public Radio, Sheldon vows to destroy Kripke, while Wolowitz tries not to destroy his new relationship with Bernadette.
Penny gets help from Sheldon in order to understand what Leonard's work is, while Wolowitz develops a jealousy when Leonard starts hanging out with his new girlfriend.
A Christmas visit from his mother has Leonard discovering she's kept a lot of news from him that she shares with Sheldon and worrying if she'll approve of his romance with Penny.
Leonard is aghast to find out a secret of Penny's: she believes in psychics. Meanwhile, Sheldon tries to assist Koothrappali in picking up a girl at a university mixer.
Leonard can only bring one guest on a trip to see CERN's Large Hadron Collider (the world's largest and highest energy particle accelerator) in Switzerland on Valentine's Day.