Night Vision by Randy Wayne White (Doc Ford Series, Book 18)

The Red Citrus Trailer Park is inhabited mostly by illegal laborers. But the steroid-powered park manager and his grotesquely muscular girlfriend want to sell the park for some easy money-and they'll do whatever it takes to drive the residents out. Their problem is a young girl who the laborers believe talks to God. When the girl witnesses the manager dumping a corpse into a lake, he knows that she has to be silence permanently.

The girl's only hope for survival: marine biologist Doc Ford, who must search through an underground nation, trek through wildlife, and defeat an assortment of bad guys...and hope he reaches her in time.