Working from a graphic novel by John Wagner and Vince Locke, screenwriter Josh Olson creates a modern-day parallel to all those classic Westerns (from "The Gunfighter" to "Shane" to "The Shootist" to "Unforgiven") in which world-weary gunslingers naively think they can hang up their six-shooters -- at least until, inevitably, their violent pasts catch up with them.