The Deep Abiding (Ryan Lock 10) by Sean Black

Retired US Marine Ty Johnson is hired to protect a young reporter investigating the brutal, decades-old murder of a young African American woman in the Florida Everglades.
The small town of Darling, Florida, on the edge of the Everglades, seems like an idyllic place to raise a family or retire in peace. But something deeply sinister lies beneath the surface, and military veteran Ty soon finds himself plunged into a living nightmare that will test the very limits of his endurance