Thieftaker by D.B. Jackson
Boston, 1765: The British Crown imposes onerous taxes on the thirteen colonies, and intrigue swirls around firebrands like Samuel Adams and the Sons of Liberty. For Ethan Kaille, a conjurer who makes his living tracking down thieves, politics is for others...until he is asked to recover a necklace worn by the murdered daughter of a prominent family. A man with a dark past, Ethan can ill afford to turn this case down. But taking the case means facing the most powerful members of Boston's high society and its seamy underbelly. And behind it all, another conjurer waits, who has already killed in the service of powerful masters. Ethan is in way over his head, hopelessly overmatched by the deadly spell craft of someone he cannot even see.