Kate Graham and her twin brother, "Trooper Billy," as he is affectionately called, are the guests of Col. Blake at a western army post. Lieut. Blake, the Colonel's son, is in love with Kate. Sun Jewel is the mother of Sunrise Beek, a half-breed. A refusal by the colonel to recognize her son as his own causes her to inform the half-breed of his parentage. The latter demands recognition by his father, but is ordered off the post. Beek secures vengeance by slaying "Trooper Billy," knowing the colonel loves the boy as his own. Stetlow, scout, sent out to find Billy, returns with the boy's hat. Kate is heartbroken and Stetlow thrusts his advances upon her, to be driven from the room by Lieut. Blake, who arrives in time to witness the incident. Beek and Stetlow plan to deliver the fort into the hands of the Indians. A detachment sent to look for "Trooper Billy" is divided by a ruse, one-half of it turning back toward the post. A plot to wipe out Lieut. Blake's detachment is overheard by Kate, who is disguised in her twin brother's clothes. By heroic work, Kate rescues Lieut. Blake and his men and all return to the post in time to save it from falling into the hands of the Indians. Beek, believing that Stetlow has betrayed him, makes his way into the fort, where he finds his man in the colonel's room. A terrific knife encounter takes place, which ends in the death of both men. Stetlow, however, lives long enough to receive Kate's forgiveness. Kate's bravery is lustily cheered by the soldiers.