Sutekh: Book 4 of The Eliana Brennan Series in Bloomington, MN

Eliana has met witches before, but she never expected to run into them while on a case for her new employer - Homeland Security. Witches are supposed to keep their existence unknown to humans. So, why has one suddenly gone on a killing spree leaving evidence of spells and magic in his or her wake for the human authorities to find?