The Last Hours Tome 2 (Relié)

Secrets consume even the truest love. Cordelia Carstairs seems to have everything she ever wanted. She is engaged to James Herondale, the boy she has loved since childhood. She has a new life in London with her best friend, Lucie Herondale. And she bears the sword Cortana, a legendary hero's blade. But the truth is that James is in love with the mysterious Grace Blackthorn, while Cortana burns Cordelia's hand when she touches it.
Even worse, a serial murderer is targeting the Shadowhunters, Cordelia, James and Lucie must follow their trail through the city streets. All the while each is keeping a shocking secret - and James fears that he himself may be the killer they seek.