In a secret world where half-angel warriors are sworn to fight demons, parabatai are partners in battle; best friends. Parabatai can be everything to each other - but they can never fall in love.

Emma Carstairs is a warrior, a Shadowhunter. Alongside her parabatai, Julian Blackthorn, she patrols Los Angeles, where vampires party and faeries - the most powerful of supernatural creatures - teeter on the edge of war with Shadowhunters. When the bodies of humans and faeries are found murdered in the same way Emma's parents were when she was a child, an uneasy alliance is formed. They must solve the murders . . . before the murderer targets them.

Each clue Emma unravels uncovers more secrets. What has Julian been hiding from her all these years? Why does Shadowhunter Law forbid parabatai to fall in love? Who really killed her parents - and can she bear to know the truth?