Sebastian Morgenstern is on the move, systematically turning Shadowhunter against Shadowhunter. When one of the greatest betrayals the Nephilim have ever known is revealed, Clary, Jace, Isabelle, Simon, and Alec must flee - even if their journey takes them deep into the demon realms, where no Shadowhunter has set foot before, and from which no human being has ever returned. Love will be sacrificed and lives lost in the thrilling and long-awaited final installment of the best-selling and acclaimed Mortal Instruments.