The Devil's Punchbowl book by Greg Iles

Penn Cage was elected mayor of Natchez, Mississippi—the hometown he returned to after the death of his wife—on a tide of support for change. But two years into his term, casino gambling has proved a sure bet for bringing in new jobs and fresh money to this fading jewel of the Old South. But deep inside the Magnolia Queen, a fantastical repurposed steamboat, a depraved hidden world draws high-stakes players with money to burn on their unquenchable taste for blood sport and the dark vices that go with it.

When a childhood friend hands him blood-chilling evidence, Penn must beat the odds tracking a sophisticated killer who counters his every move, placing those nearest to him—including his young daughter, his renowned physician father, and a lover from the past—in grave danger, and all at the risk of jeopardizing forever the town he loves.