Carrie (AnnaSophia Robb), Mouse (Ellen Wong), Maggie (Katie Findlay), and Walt (Brendan Dooling) decide to go to their senior prom - at The Waldorf Astoria - together for a final hurrah. Larissa (Freema Agyeman) offers Carrie an opportunity that makes her rethink her plans for the next year. Mouse learns a secret about Donna LaDonna (Chloe Bridges) that could threaten her reign as queen bee. Meanwhile, Sebastian (Austin Butler) hides a big decision from Carrie.