Doctors Leonard Hofstadter & Sheldon Cooper (Johnny Galecki & Jim Parsons) are brilliant physicists – masterminds of their CalTech laboratories, but socially challenged in the non-theoretical real world. Enter beautiful, street-smart neighbor, the actress/waitress Penny (Kaley Cuoco), 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 grown comfortable with a female companion, entering into a signed “Relationship Agreement” with neurobiologist Amy Farrah Fowler (Mayim Bialik). In their free time, Leonard and Sheldon continue to enjoy weekly trips to the comic book store and fantasy role-playing games with their ever-expanding universe of friends, including fellow scientists Rajesh Koothrappali (Kunal Nayyar), Howard Wolowitz (Simon Helberg), and Howard’s microbiologist wife, Bernadette (Melissa Rauch).