Darkness has descended on the Shadowhunter world. Chaos and destruction overwhelm the Nephilim as Clary, Jace, Simon, and their friends band together to fight the greatest evil they have ever faced: Clary's own brother. Nothing in the world can defeat Sebastian, but if they journey to the realm of demons, they just might have a chance. Lives will be lost, love sacrificed, and the whole world will change. Who will survive?