The return - Michael Gruber

From the New York Times bestselling author of The Book of Air and Shadows, the story of one man's fearless quest for revenge among some of the world's most dangerous criminals.The real Richard Marder would shock his acquaintances, if they ever met him. Even his wife didn't know the real man behind the calm and cultured mask he presents to the world. Only an old army buddy from Vietnam, Patrick Skelly, knows what Marder is capable of.
Then a shattering piece of news awakens Marder's buried desire for vengeance, and with nothing left to lose, he sets off to punish the people whose actions, years earlier, changed his life. Uninvited, Skelly shows up and together the two of them raise the stakes far beyond anything Marder could have envisioned.
As Marder and Skelly head toward an apocalypse of their own making, Marder learns that good motives and a sense of justice can't always protect the people a man loves...