Nemesis

"Evan Smoak, having shaped his life with a rigid set of rules, finds himself at odds with his oldest friend in the world, where principles are in conflict with honor--and everyone is the loser. At one time, Evan Smoak was a highly successful black ops assassin known as Orphan X, dedicated to a rigid set of operational rules. Now, even after breaking with the government program, going deep underground, and remaking his life, Smoak is dedicated to his assassin's Ten Commandments. But for the first time, those principles have put him on a collision course with the man who might be his best friend in the world, Tommy Stojack. Stojack, a gifted gunsmith who has created much of Evan's own weapons and combat gear, has apparently crossed one of Evan's sharply delineated lines. When Evan decides to go to his workshop and have it out with Tommy, Evan finds himself under attack by a group attempting to ambush and kill him. But, with all his training and skills, Evan is extremely hard to kill--and the dispute explodes into open warfare between him and Tommy. Now Evan has no choice, in his mind, than to track down and face down his only friend"--