Scapegrace diver Tiller Galloway finds the inner space of limestone caves as risky as the open-ocean deeps probed in his three previous outings (Louisiana Blue, 1994, etc.). With precious little going for him on North Carolina's Outer Banks, Tiller willingly heads to Florida when Monica Kusczk asks for his help after the supposedly accidental death of her husband Bud (with whom Galloway served as a SEAL in Vietnam). Also on the trip to Tallahassee is Tiller's sullen teenaged son Tad, who has run away from his demanding mother. Once in the Sunshine State, Tiller helps manage the diving equipment store owned by his dead friend, takes up the dangerous sport of cave diving, and starts a relationship with the receptive Monica. In short order, Tiller finds that the pitch-dark caverns created by aquifers are treacherous venues and no place for amateurs, and learns from a hardcase emissary that Bud had been laundering money for a Colombian coke cartel and that he's expected to do the same. Meantime, Tiller (convinced that Bud's demise was no mishap) determines that a socially prominent local has been diverting water from underground springs to his closely guarded nursery, where, among other cash crops, he's hydroponically cultivating coca leaves and marijuana. With two sets of villains on his case, the renegade mariner (who's done time himself for drug-running) calls in the feds. The overeager DEA makes a shambles of the resultant raid, and Monica (whom Tiller was beginning to love) is gunned down in a crossfire. With unexpected assistance from Tad, however, Galloway survives the wild shootout. When the heat dies down, he returns home to Cape Hatteras with his son, sadder, wiser, and with nearly $1 million in untraceable greenbacks. White-knuckle diving scenes, constant action, and a raffish antihero whose motives lie well below the surface make the latest chapter in the motley tale of Tiller Galloway a welcome addition to Poyer's offbeat series.