Gun from the outside

Dan Wade left Big Bill Krask's Double K Ranch because there was little chance for advancement when everything Big Bill did was to benefit his son and heir, Little Bill. Then a letter comes to Wade in Abilene from Marshal William Krask, asking him to come back and help out. Wade returns to find that much has changed: The marshal is not Big Bill, but his son Little Bill. And the great enemy to law and order is Big Bill and his gang of hardcases.