Sheldon and Bert collaborate on a research project; Penny and Bernadette coach Raj on how to navigate his relationship with Ruchi.
Sheldon stresses about picking a wedding date. Koothrappali and Stuart compete to win the heart of Bernadette’s new coworker, Ruchi.
Leonard and Howard enlist Barry Kripke to help after they learn Sheldon betrayed them by working with the military behind their backs.
Liza is drawn into her author's Upper East Side life, forcing her worlds to collide; Kelsey comes to Lauren's rescue.
Liza and Maggie meet Josh in Ireland. Kelsey is forced to play nice with a new colleague. Charles’s personal life is thrown into the spotlight.