City of Lost Souls is the fifth book in The Mortal Instruments series by Cassandra Clare.

Clary and the rest of the group manages to gain the assistance of the Seelie Queen, but in return they have to obtain and hand over two Faerie rings that would allow the wearers to communicate telepathically.

Desperate, Clary agrees to the terms and while searching for the rings in a Shadowhunter library, accidentally observes Jace enter the library and speak in friendly terms with Sebastian (Who is actually "Jonathan Morgenstern", Valentine's half-demon blooded son) - which confuses Clary, who had been hiding during the conversation.

Meanwhile, Jordan Kyle and Maia Roberts, and separately Simon and Isabelle, are growing closer.

Unable to reach Sebastian, Clary uses the Angel blade and stabs Jace, believing that it will not kill him as his heart is more good than evil.

When she's finally allowed to visit Jace, she learns that stabbing him with Glorious has filled him with "Heavenly fire", which will burn anything he touches whenever he gets an adrenaline rush.

[4] Kirkus Reviews wrote a mixed review for City of Lost Souls, writing that the sections focusing on Clary's POV "[focus] on her wardrobe instead of her character development" while also stating that "Fans of the familiar will find this an unchallenging goth-and-glitter pleasure.