Against All Enemies (A Jonathan Grave Thriller) by John Gilstrap

Jonathan Grave finds it hard to believe that a fellow combat vet has gone rogue, killing American agents and leaking sensitive intel to hostile foreign interests. With black ops assassins on the trail of his old friend, Grave sets out to get to him first. He finds far more than he bargained for.  Not only the wily operative, but evidence of a conspiracy so dangerous, so far-reaching, that an unthinkable tragedy is in-motion. Grave and his elite team of specialists must expose a deadly high-level secret —and do it in time to avert a catastrophe of historic