Ashes and Arsenic - Preternatural Affairs, #6

Agent Cèsar Hawke is in his element when he's investigating magical crime. And with his boss out of town, Cèsar gets to pick which cases he works on. He's bent on doing nothing involving demons, zombies, or fallen angels this time. Instead, he's going to find the witch who used magic to rob a bank. Easy stuff. Cèsar plans to catch the perp before his boss gets home. But when he digs into the robbery, he finds much more than missing money.
He also finds a deadly turf battle between two covens and a trail of bloody violence. A trail that leads directly to his brother, Domingo Hawke. Domingo wants Cèsar's help taking down his enemies. Forget that Cèsar works for the Office of Preternatural Affairs, forget allegiances, forget pesky "contracts" and "conduct." Domingo is calling in a favor and the Hawke family is too tight to refuse. Blood is the most powerful ingredient in any witch's spell, after all.