Ocean Prey (Lucas Davenport Series #31)
"An off-duty Coast Guardsman calls in some suspicious behavior from a nearby boat. It's a snazzy craft that slows to pick up a surfaced diver--a diver who was apparently alone, without his own boat, in the middle of the ocean. None of it makes sense, and his hunch is proved right when all three Guardsmen who come out to investigate are shot and killed. They're federal officers killed on the job, which means the case is the FBI's turf. When the FBI investigation stalls out, they call in Lucas Davenport. And Davenport will need to bring in every asset, including a detective with a fundamentally criminal mind: Virgil Flowers"--Page 4 of cover.