Welsh-Huggins’s strong fourth Andy Hayes mystery (after 2016’s Capitol Punishment) finds the Columbus, Ohio, PI still struggling with personal relationships but a bit more confident as an investigator. When prostitute Jessica Byrnes disappears when five young women have already been murdered by a serial killer, Andy interviews a lot of people, including Det. Larry Schwartzbaum, who handled the missing-person call about Jessica; attorney Karen Feinberg, who once represented Jessica; and Jessica’s sleazy stepfather, Jimmy Wooding. Andy is surprised by a call from Congresswoman Darlene Bardwell, who’s concerned with human trafficking and wants to help. Just as a picture emerges of a troubled and frightened Jessica, Andy runs afoul of brutal pimp Bronte Patterson. Welsh-Huggins handles equally well the complex motivations of politicians, social workers, cops—those who are supposed to help victims—and of those who prey on them, such as pimps and johns. This series gets better with each book.