City of Fallen Angels (The Mortal Instruments #4)

Simon, Daylighter vampire teen is protected by the Mark of Cain, a pillar of fire from Heaven blazes attackers into salt, but an enemy gets at him through his first love Clary, who must face consequences, and maybe lose Jace. A Greater Demon infects nights of her Shadowhunter beloved for control, and sends grey-garbed minions for Simon himself.