Unfaithful Servant — Tom Casey

Unfaithful Servant tells the story of Jack Harris, recently retired CIA officer, and Frank Warren, FBI agent and Jack's childhood friend. When they were boys, Jack and Frank witnessed a murder and after a terrifying confrontation with the killer, they made a vow to each other of secrecy and fealty.
Last based in Baghdad, Jack Harris lost his fiancé, an army major, to a landmine explosion on the road to Fallujah. The Humvee she was driving did not have sufficient armor. Known for fearlessness and brilliant tradecraft, Jack retires to America. Terrorist bombings, including an attack on the Statue of Liberty, raise suspicions in Frank Warren that his friend is behind them. He wants to know why. The two meet for a game of golf. Invoking the “Boathouse Vow,” Frank demands to know where Jack is going with these attacks. He will learn by the end of the game.
Unfaithful Servant is a fast paced thriller that examines the potential for a single person to change the course of world events.