Bass, Sally, and baby Lil pay a visit to his sister Gracie and her family, the Whitworths, at their new ranch called the Circle W in northern Colorado. Unbeknownst to them, a range war is raging in Wyoming just to the north of them, pitting the cattle barons of the Wyoming Territory against the smaller ranchers, farmers, and sheepmen that have come to settle there. The Wyoming Cattle Growers Association, headquartered in Cheyenne, has hired an army of paid gunmen led by one Tom Horn to see to it that the smaller concerns are encouraged to leave the Territory. Horn and his gang of thugs are deputized by a corrupt sheriff, which makes their actions legal and qualifies them as Regulators rather than vigilantes or gangsters. Horn and his gang of killers begin a murderous campaign accusing the smaller ranchers of cattle theft with little or no proof. The result is wholesale killings. Hangings of men and women and cold-blooded assassinations of men and boys. Being close to the border and only a day’s ride from Cheyenne, The Circle W comes under the Regulator's purview. Borders and state lines mean nothing to these villains, and Bass and his sister’s family are soon embroiled in one of the most violent and deadly chapters in frontier history. And Bass makes a lethal enemy along the way.