Leonard and Sheldon are brilliant physicists - wizards in the laboratory, but socially challenged outside of it. Enter beautiful, street-smart neighbor, Penny, who aims to teach them a thing or two about life. Despite their on-again, off-again relationship in the past, Leonard believes he's found true love with Penny. Even Sheldon has found a female companion - entering into a "Relationship Agreement" with neurobiologist Amy Farrah Fowler. In their free time, Leonard and Sheldon continue to enjoy frequent trips to the comic book store and fantasy role-playing games with their ever-expanding universe of friends, including fellow scientists Raj and Howard, and Howard's adorable microbiologist wife, Bernadette.