Weeks, Brent. Kylar chronicles #1

"After the war that cost him so much, Kylar Stern is broken and alone. He's determined not to kill again, but an impending amnesty will pardon the one murderer he can't let walk free. He promises himself this is the last time. One last hit to tie up the loose ends of his old, lost life. But Kylar's best, and maybe only, friend, the High King Logan Gyre, needs him. To protect a fragile peace, Logan's new kingdom, and the king's twin sons, he needs Kylar to secure a powerful magical artifact that was unearthed during the war. With rumors that a kakari may be found, adversaries both old and new are on the hunt. And if Kylar has learned anything, it is that ancient magics are better left in the hands of those he can trust. If he does the job right, he won't need to kill at all. This isn't an assassination, it's a heist. But some jobs are too hard for an easy conscience, and some enemies are so powerful the only answer lies in the shadows"--