In the vibrant city-state of Castellane, the richest of nobles and the most debauched of criminals have one thing in common: the constant search for wealth, power and the next hedonistic thrill.

Kel is an orphan, stolen from the life he knew to become the Sword-Catcher - the body-double of a royal heir, Prince Conor Aurelian. He has been raised alongside the prince, trained in every aspect of combat and statecraft. He and Conor are close as brothers, but Kel knows he has one destiny: to die for Conor. No other future is possible.

Lin Caster is one of the Ashkar, a small community who still possess magical abilities. By law, they must live behind walls in the city, but Lin, a physician, ventures out to tend to the sick and dying of Castellane. Despite her skills, she cannot heal her best friend Mariam without access to forbidden knowledge.

After a failed assassination attempt brings Lin and Kel together, they are drawn into the web of the mysterious Ragpicker King, the criminal ruler of Castellane's underworld. He offers them each what they want most; but as they descend into his world of intrigue and shadow, they discover a conspiracy of corruption that reaches from the darkest gutters of Castellane to the highest tower of its palaces. As long-kept secrets begin to unravel, they must ask themselves: is knowledge worth the price of betrayal? Can forbidden love bring down a kingdom? And will Lin and Kel's discoveries plunge their nation into war - and the world into chaos?