Fallen - Smoke & Magic, #1

How do you fight true evil when you have nothing? A fatal error hurls an angel from Heaven's grace. Lost and drowning in the modern world, Cassiel struggles to keep her head above water. Everything feels too bright, too loud, too fast. However, survival in an uncaring city is the least of her worries. When a friend is murdered and a young elven girl is kidnapped, Cassiel must face the dark realities of the world.
Supernatural drugs, gangs, and mortal cruelty awaken a sleeping fury in the angel whose duty was standing as a guardian. Alongside unlikely allies, Cassiel races to uncover the truth of the crimes only to discover the reality is far worse than she could have imagined.