Alec, Jace and Isabelle make a plan to finally get Clary back and stop Jonathan, much to Luke's and Simon's chagrin; Magnus struggles to deal with his father's reappearance; Maia must make a tough decision that could affect the rest of her life.
Anna, Elsa, Kristoff, Olaf and Sven leave Arendelle to travel to an ancient, autumn-bound forest of an enchanted land. They set out to find the origin of Elsa's powers in order to save their kingdom.