Clockwork Princess (The Infernal Devices, #3)

Danger and betrayal, secrets and enchantment in the breathtaking conclusion to the Infernal Devices trilogy.

Tessa Gray should be happy - aren't all brides happy?
Yet as she prepares for her wedding, a net of shadows begins to tighten around the Shadowhunters of the London Institute.
A new demon appears, one linked by blood and secrecy to Mortmain, the man who plans to use his army of pitiless automatons, the Infernal Devices, to destroy the Shadowhunters. Mortmain needs only one last item to complete his plan. He needs Tessa. And Jem and Will, the boys who lay equal claim to Tessa's heart, will do anything to save her.