To save her mother’s life, Clary must travel to the City of Glass in Idris, the ancestral home of the Shadowhunters — never mind that entering the city without permission is against the law, and breaking the law could mean death. To make things worse, she learns that Jace does not want her there, and her best friend, Simon, has been thrown in prison by the Shadowhunters, who are deeply suspicious of a vampire who can withstand sunlight.

As Clary uncovers more about her family’s past, she finds an ally in mysterious Shadowhunter called Sebastian. With Valentine (the main bad guy) mustering the full force of his power to destroy all Shadowhunters forever, their only chance to defeat him is to fight alongside their

eternal enemies. But can Downworlders (a Downworlders is a creature like a werewolf), a vampire, the fare folk (the fare folk is faeries and warlocks) and Shadowhunters put aside their hatred to work together?

 While Jace realizes exactly how much hs willing to risk for Clary, can she harness her newfound powers to help save the Glass City — whatever the cost?                   

Jace is a blonde 16 year old Shadowhunter with gold eyes due to having extra angel blood. 

When we start the book we see that Jace does not want Clary to go to the Shadowhunter homeland of Idris. He gets Simon to help him and they get attacked by the Forsaken and they portalled to Idris. When they get there they are greeted by the Penhallows and Sebastian Verlac.