Lord of Shadows by Cassandra Clare

Emma Carstairs has learned that the love she shares with her parabatai, Julian Blackthorn, isn’t just forbidden—it could destroy them both. She knows she should run from Julian. But how can she when the Blackthorns are threatened by enemies on all sides? Their only hope is the Black Volume of the Dead, a spell book of terrible power. Everyone wants it. Only the Blackthorns can find it. Spurred on by a dark bargain with the Seelie Queen, Emma; her best friend, Cristina; and Mark and Julian Blackthorn journey into the Courts of Faerie, where glittering revels hide bloody danger and no promise can be trusted. Meanwhile… Read more.