Leonard and Sheldon are brilliant physicists -- geniuses in the laboratory, but socially challenged everywhere else. Enter their 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 and they have finally gotten engaged. Even Sheldon has found a female companion, entering into a "Relationship Agreement" with neurobiologist Amy Farrah Fowler, who recently asked him to take a break because she is frustrated with how slowly their relationship is progressing. 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, Howard and Howard's adorable microbiologist wife, Bernadette.