The Oath of His Office (1912)

Bob Graham gains the consent of Grace Allen to marry before he leaves for the fall round-up. Bob takes with him a locket given him by Grace as a token of remembrance. Jed Brown, who has also loved Grace, goes with the punchers across the range and when opportunity offers steals the locket and forges a note which he returns and gives to Grace, making her believe that Bob has jilted her. Womanlike, she turns her affections to Jed and they are married. Bob learns of the trick and makes a solemn vow someday to get even.