The Devil's Punchbowl by Greg Iles

As a prosecutor in Houston, Penn Cage sent killers to death row. But as mayor of his hometown – Natchez, Mississippi – Penn will face his most dangerous threat. Urged by old friends to try to restore this fading jewel of the Old South, Penn has ridden into office on a tide of support for change. But in its quest for new jobs and fresh money, Natchez has turned to casino gambling, and now five steamboats float on the river beside the old slave market, like props from Gone With the Wind.