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.

In season five, Penny and Leonard's relationship is relaunched in full "beta test" mode, while Sheldon, Howard, and Raj discover the feminine mystique is something that cannot be easily graphed or calculated. As Sheldon makes begrudging amendments to his "Relationship Agreement" with his "friend-who-happens-to-be-a-girl" Amy Farrah Fowler, Raj contemplates an arranged marriage, and Howard is all-systems-go for both is NASA space launch and wedding to the spirited Bernadette.