By Way of Pain by J.M. Dabney

Double lives were just the way it was for a man like me. By day I was a man with a reputation above reproach. Even assassins needed backup plans. For fifteen years, life was going without a hitch until I had to take out a witness. When it was time to kill him, beautiful eyes filled with fear urged me to do something else. Yet, in order to do that, I had to break him, and by way of pain, my captive would experience pleasure he’d never dreamed.