Tessa Gray, a sixteen-year-old American girl, is traveling alone to Victorian London and runs afoul of the city’s sordid supernatural underworld. Rescued by the Shadowhunters of the London Institute, she quickly finds herself caught up in an intrigue that may very well destroy her new friends—including the two enigmatic young men, Jem and Will, who have taken her under their wing...

Tessa Gray has found friends among the Shadowhunters, supernatural protectors of mankind who possess angelic blood. But Tessa's new life is threatened when some members of the Clave challenge Charlotte's leadership and pressure her to resign as head of the London Institute. If Charlotte is forced out, Tessa will be forced to leave as well due to her warlock blood, making her easy prey for the still-at-large Magister. As Tessa and her handsome Shadowhunter escorts, Will and Jem, journey far and wide to unravel the Magister's secrets, they quickly learn that they have no secrets from the vengeful Magister...and nowhere is safe...

The threat of Mortmain's Infernal Devices looms as the Shadowhunters race to work out a way to counteract the mechanical monsters. Meanwhile, plans for Tessa''s marriage to Jem are underway, despite her fiancé''s failing health and the unresolved feelings between her and Will. When Tessa is captured, Will must leave his comrade behind to save the woman they both love... But with the final missing piece-Tessa herself-in Mortmain''s possession, can anything stop his plot for revenge?