The Knox-Waterton feud is reaching a bloody crisis in the far-away mountains, when Esther Hale, from a peaceful New England village, arrives upon the scene of the trouble and becomes an unconscious factor in a war that has raged over a quarter of a century. Brian Knox, who has the heritage of leadership, is at once struck by the simple beauty of the New England girl, and her spiritual vitality as a religious factor causes him to turn aside from vengeance and listen to her reading the Scriptures, particularly her frank interpretation of the Sixth Commandment, "Thou Shalt Not Kill." Later, Brian, the last of his race, enlists in the army and Earl Waterton becomes a recruit in the same company. Attempt at desertion causes Earl to serve a two years' sentence in the military prison, and while working there on a rock pile, he is under the surveillance of Brian Knox, who gives him an opportunity to escape, with the hope that he may have the long-sought opportunity for killing him. This waited-for moment arrives, and as Brian throws his gun into range, catching the sight, his thoughts flash back to the green hills of Kentucky, to Esther Hale, and the big "six" she had him carve upon the old chestnut tree to remind him of the commandment she had taught him. He halts his man and frankly tells him he cannot kill him. He offers him his hand, and in the fervent clasp that follows, the Knox-Waterton feud ends forever.
—Moving Picture World synopsis