The Last Hours. Book II. The Iron Chain

"Cordelia Carstairs seems to have everything one could ever dream of. She is engaged to James Herondale, whom she has loved since childhood.
Her best friend, Lucy Herondale, is by her side, as is her loyal sword — Cortana. And her father, whom Cordelia loves so much, has finally come home. But this is merely a festive façade. In reality, everything is much darker.
Marriage to James is a lie, necessary to save Cordelia's reputation. Cortana burns her mistress's hand every time she touches it. And her father's return did not go as hoped.
London is also restless. A serial killer haunts the Shadowhunters on the dark streets of London… Many have already fallen at his hands.
Cordelia, James, and Lucy are trying to track down the killer and keep their secrets — each their own, terrifying secrets that could irrevocably change everything."