Magic Stars by Ilona Andrews

Scarred, solitary Derek Gaunt has separated from his Pack, and is truly a lone wolf. With no family he answers to no one; but is fiercely loyal to a chosen few. So, when several of those close to him are murdered, he’ll stop at nothing to hunt their killer through the magic-drenched streets of Atlanta.

Never one to be left on the sidelines, equally determined—some might say stubborn—Julie Lennart-Olsen soon joins in his pursuit; and what began as revenge turns into a race to save the city. Their search pits them against powers they never imagined and magic so old, it predates history. It may cost Derek his life, but there are things for which even he would risk everything.