Physicists Leonard and Sheldon find their nerd-centric social circle with pals Howard and Raj expanding when aspiring actress Penny moves in next door.
Sheldon and Amy await big news. Meanwhile, Penny and Leonard have some big news of their own. Also, Howard and Bernadette face the stressful challenge of leaving their kids for the first time and Raj makes a new friend, as the gang travels together into an uncharted future.