Sanford, John: Ocean Prey (Lucas Davenport #31/Virgil Flowers #13)

An off-duty Coast Guardsman is fishing with his family in the Atlantic just off south Florida when he sees, and then calls in, some suspicious behavior in a nearby boat. It's a snazzy craft, slick and outfitted with extra horsepower, and is zipping along until it 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 unless there's something hinky going on, and his hunch is proven correct 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's investigation stalls out, Lucas Davenport of the U.S. Marshals Service gets a call. The case turns even more lethal and Davenport needs to bring in every asset he can find, including a detective with a fundamentally criminal mind: Virgil Flowers.