Sixteen-year-old Clary continues trying to make sense of the swiftly changing events and relationships in her life as she becomes further involved with the Shadowhunters and their pursuit of demons and discovers some terrifying truths about her parents, her brother Jace, and her boyfriend Simon.

Still pursuing a cure for her mother's enchantment, Clary uses all her powers and ingenuity to get into Idris, the forbidden country of the secretive Shadowhunters, and to its capital, the City of Glass, where with the help of a newfound friend, Sebastian, she uncovers important truths about her family's past that will not only help save her mother but all those that she holds most dear.

When Jace vanishes with Sebastian, Clary and the Shadowhunters struggle to piece together their shattered world and Clary infiltrates the group planning the world's destruction.