Defender by Christine Pope

Murder...mayhem...and no place to hide.
Ever since the moment when Kate Campbell realized she wants more, deserves more, she's known it would come to this - delivering divorce papers to her estranged husband. Creepy silence greets her knock, and she finds him brutally murdered, arcane symbols slashed across the walls in blood.
The last thing Detective Jack Sandoval needs is another witch-related crime to sweep under the rug. As the de la Paz witch clan's expert in defensive magic, Jack knows there is some deeper form of ritual dark magic involved...and one look into Kate's beautiful, stricken face tells him she isn't the culprit.
He also knows this isn't any ordinary ritual murder. It's the tip of a cold iceberg of revenge that not only threatens Kate's life, but could reach deep into the clan to rip out its heart.
When the two of them take refuge at Jack's isolated house, deep in the Arizona desert, desire creates a magic all its own. But the killer will use any means to draw Kate into the open...where the fight for her life could be only the beginning of a more brutal war to come.