Alec, Jace and Isabelle make a plan to finally get Clary back and stop Jonathan—much to Luke's and Simon's chagrin. Meanwhile, an emotionally raw Magnus struggles to deal with his father's reappearance and Maia must make a tough decision that could affect the rest of her life.

Jonathan begins his reign of vengeful terror as the Shadowhunters try to find a way to stop him. With only one hope, Clary must make a sacrifice that could have long-lasting implications for all. Meanwhile, wedding bells are in the air for one special couple.