City of Fallen Angels by Cassandra Clare

The Mortal War is over, and Clary Fray is back home in New York, excited about all the possibilities before her. She's training to become a Shadowhunter and to use her unique power.

Her mother is getting married to the love of her life. Downworlders and Shadowhunters are at peace at last. And—most important of all—Clary can finally call Jace her boyfriend.

But nothing comes without a price...