With Chuck and Sarah's engagement party looming, the former invites the latter's old spy team into town for the event. While the Cat Squad is in Burbank, one of their old missions comes to the forefront and all hands are on deck to save the day. One of the Cats is a traitor, and it turns out not to be the one Sarah had suspected all along.
Morgan is locked up in Castle with one of the Cats, Carina. Yes, it is the same Carina we met back in season one that Morgan was once smitten with. Carina tries to sabotage Morgan's relationship with Alex, but fails miserably because Morgan and Alex finally say that they love each other.
Sarah is still upset that she doesn't have any friends or family to come to the wedding. Her first reaction to Chuck inviting the Cat Squad is to get angry, but after they weed out the traitor, she invites the other two to be her brides maids. She also asks Ellie to be her maid of honor, and of course Chuck's sister accepts.