The situation at the London Institute has never been more precarious. With Mortmain and his clockwork army still threatening, the Council wants to strip Charlotte of her power and hand the running of the Enclave over to the unscrupulous and power-hungry Benedict Lightwood. In the hope of saving Charlotte and the Institute, Will, Jem, and Tessa set out to unravel the secrets of Mortmain's past--and discover unsettling Shadowhunter connections that hold the key not only to the enemy's motivations, but also to the secret of Tessa's identity. Tessa, already caught between the affections of Will and Jem, finds herself with another choice to make when she learns how the Shadowhunters helped make her a "monster." Will she turn from them to her brother, Nate, who has been begging her to join him at Mortmain's side? Where will her loyalties--and love--lie? Tessa alone can choose to save the Shadowhunters of London...or end them forever.er a clockwork demon bearing a warning for Will, they realize that the Magister himself knows their every move--and that one of their own has betrayed them. Tessa finds her heart drawn more and more to Jem, though her longing for Will, despite his dark moods, continues to unsettle her. But something is changing in Will--the wall he has built around himself is crumbling. Could finding the Magister free Will from his secrets and give Tessa the answers about who she is and what she was born to do? As their dangerous search for the Magister and the truth leads the friends into peril, Tessa learns that when love and lies are mixed, they can corrupt even the purest heart.