Keller is a killer. Professional, cool, confident, competent, reliable. The consummate pro. The hit man's hit man.
But he is a complex person: understandably guarded and reclusive, icy and ruthlessly efficient, he is also prone to loneliness, self-doubt, and career worries. Indeed, he is going through a full-fledged mid-life crisis. Keller may be a crack assassin, but he is also an all-too-human being.
As Keller goes about his rounds, fulfilling his contracts, he learns a few crucial truths about himself and the ways of the normal world and winds up a wiser (if not a better) man.