Emerald Blaze by Ilona Andrews

As Prime magic users, Catalina Baylor and her sisters have extraordinary powers—powers their ruthless grandmother would love to control. Catalina can earn her family some protection working as deputy to the Warden of Texas, overseeing breaches of magic law in the state, but that has risks as well. When House Baylor is under attack and monsters haunt her every step, Catalina is forced to rely on handsome, dangerous Alessandro Sagredo, the Prime who crushed her heart.

The nightmare that Alessandro has fought since childhood has come roaring back to life, but now Catalina is under threat. Not even his lifelong quest for revenge will stop him from keeping her safe, even if every battle could be his last. Because Catalina won’t rest until she stops the use of the illicit, power-granting serum that’s tearing their world apart.