To save her mother's life, Clary must travel to the City of Glass, 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 Clave, 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 Sebastian. With Valentine 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 and Shadowhunters put aside their hatred to work together? While Jace realizes exactly how much he's willing to risk for Clary, can she harness her newfound powers to help save the Glass City — whatever the cost?
Love is a mortal sin and the secrets of the past prove deadly as Clary and Jace face down Valentine in the third installment of the New York Times bestselling The Mortal Instruments.
Part One: Sparks Fly Upward
Part Two: Stars Shine Darkly
Part Three: The Way to Heaven
Epilogue: Across the Sky in Stars
- Clary Fray - the main protagonist of the series, Clary's gift is crucial to their victory against her father, Valentine.
- Jace Morgenstern - a very skilled Shadowhunter who, upon realizing that his father is alive and is the evil Valentine Morgenstern, is having problems figuring out who he wants to be.
- Alec Lightwood - the eldest Lightwood and Jace's parabatai; Alec's sexuality, which is frowned upon in the Nephilim society, and relationship with Magnus Bane bring up issues for himself and his family.
- Isabelle Lightwood - Alec's beautiful younger sister, Isabelle is a strong and fierce Shadowhunter, as well as a rebellious daughter.
- Valentine Morgenstern - the notorious leader of the Circle, father of Clary and Jace, and husband of Jocelyn. With the Mortal Instruments now at his disposal, Valentine puts his plans for the downfall of Shadowhunters and Downworlders in action.
- Jocelyn Fray - Clary's mother who put herself in a coma to prevent Valentine from getting answers from her.
- Maryse & Robert Lightwood - parents of the Lightwood children and heads of the New York Institute.
- Max Lightwood - the youngest Lightwood child at nine years old.
- Sebastian Verlac - a mysterious new player who meets Clary and the Lightwoods in Alicante.
- Aline Penhallow - a friend of the Lightwoods and the cousin of Sebastian Verlac.
- Amatis Herondale - Luke's sister who lives in isolation in Idris.
- Inquisitor Aldertree - the Inquisitor who replaced the recently deceased Inquisitor Herondale, Aldertree, contrary to his job, is not above blackmailing, lying, and pointing fingers at innocents to close a case.
- Madeleine Bellefleur - a friend of Jocelyn who claims to know how to help Jocelyn awake from her coma.
- Simon Lewis - Clary's best friend who was Turned into a vampire after being drawn into the Shadow World.
- Magnus Bane - the High Warlock of Brooklyn who decides to help the Conclave for Alec.
- Luke Garroway - a former Shadowhunter and now a werewolf, Luke is a close friend of Jocelyn who helped raise Clary.
- Maia Roberts - a member of Luke's New York werewolf pack.
- Raphael Santiago - leader of the New York vampire clan.
- Seelie Queen - the queen of the Seelie Court of the Fair Folk.
- Meliorn - the queen's personal knight and confidante.
- Raziel - the patron Angel of the Nephilim.
- Ithuriel - an angel imprisoned by Valentine whose blood he used on his experiments.
- The original (now hardbound) cover features Jonathan Morgenstern while in the guise of Sebastian Verlac. The repackaged (paperback) cover features Simon Lewis bloody and sitting on the ground with chains around him, signifying his imprisonment in the book, with the Agony rune behind him.
- Cassandra Clare had wanted the cover to feature Jace and Sebastian.
- The title refers to Alicante, which is often referred to as "the City of Glass".
- City of Glass was originally set to be the last book in The Mortal Instruments trilogy, but the series was later expanded to include three more books.
- The book is told from several points of views, namely: Clary, Jace, Simon, Isabelle, and Alec's.