Drs. Leonard Hofstadter (Galecki) and Sheldon Cooper (Parsons) are brilliant physicists – geniuses in the laboratory, but socially challenged everywhere else. Enter beautiful, street-smart neighbor, Penny (Cuoco), who aims to teach them a thing or two about life. Despite their on-again, off-again relationship in the past, Leonard and Penny have finally gotten married. Even Sheldon has found a female companion – entering into a “Relationship Agreement” with neurobiologist Amy Farrah Fowler (Bialik), and he recently took their relationship to the next level by proposing marriage. In their free time, Leonard and Sheldon enjoy fantasy role-playing games with their ever-expanding universe of friends, including fellow scientists Rajesh Koothrappali (Nayyar), Howard Wolowitz (Helberg) and Howard’s adorable microbiologist wife, Bernadette (Rauch), who is now adjusting to life with their new baby girl, Halley.