The fourth season of The Big Bang Theory finds Leonard (Johnny Galecki) falling for Raj's sister Priya following his break-up with Penny (Kaley Cuoco). Meanwhile, Sheldon (Simon Helberg) finds romance with a neurologist who quickly establishes herself as Penny's new best friend. As Howard and Bernadette's relationship blossoms, Bernadette finds herself plagued by Bollywood daydreams starring Raj (Kunal Nayyar).