All these answers and more are revealed in the intriguing 'Lady Midnight'.
If you can't wait for the sequel 'Lord of the Shadows', tension filled writing engages you and you like supernatural romantic fantasy served with a side of demons you should start with book one of the Mortal Instruments series, [[City of Bones by Cassandra Clare|City of Bones]]. Alternatively you might like to experience Shadowhunters steampunk style in [[The Infernal Devices: Clockwork Angel, Volume 1: The Manga (Manga Edition) by Cassandra Clare and HyeKyung Baek]]
For more demonic adventures you can immerse yourself in [[The Demon Trappers: Forsaken by Jana Oliver]] and [[Demon Road by Derek Landy]].
Alternatively, perhaps the mythology of demons and other worldly creatures will tempt you. You can read all about their genesis in the absorbing [[A Field Guide to Demons, Fairies, Fallen Angels and Other Subversive Spirits by Carol and Dinah Mack]].