Chuck has his pick of the best CIA agents for an undercover operation, but he has only one girl in mind for the job; Sarah. Casey, Morgan and Awesome team up to help Chuck win her back.

While in Europe, Sarah and Chuck realize they're traveling on a train with Spanish spies. Even though they're all alone, they decide to take on these rogue agents. Of course, this impromptu mission doesn't go smoothly. Meanwhile, Beckman orders her newest "unlikely" spy team - John Casey and Morgan Grimes - to track down the missing couple.