Deep Hex - Nick Sullivan - Bog

A new home can bring new friends... new adventures... and new dangers.
Boone Fischer and Emily Durand have settled down in the Turks and Caicos-specifically, the picturesque island of Grand Turk. But a chance encounter with a dive boat from a nearby island leads them to pull up stakes again, if only temporarily. The couple takes the Lunasea across to South Caicos-The Big South-an island with a rich history... not all of it virtuous.
An unidentified body discovered in an underwater cave system may have been the victim of a murder, but the manner of death is bizarre. Boone and Emily find themselves ensnared by events once more, but resolving this mystery may come at a steep price.