Frank held off as long as possible, but now he realized it would not do to hesitate longer. Bart was shooting in one direction, and he began shooting in the other. Through the smoke that leaped from the muzzle of his rifle he saw one man fling up his hands and plunge forward on his face. Either the men were utterly reckless, or they had not believed the boys would offer much resistance, for they exposed themselves fearlessly and rushed fiercely on the rocks behind which the trio crouched. It is possible they fancied that by shooting recklessly among the rocks they could keep the lads quiet till the barrier was reached. This was a fatal mistake for some of them. The ones who were mounted came forward more swiftly, but some of them were toppled from the saddle, others were thrown into confusion, the horses were wounded and frightened, and the riders who could escape, reined about and made haste to do so. All but the masked girl! With the utmost reckless abandon, she charged right up to the rocks. Being a girl, neither of the boys had shot toward her, or her horse. Now, however, Bart Hodge rose to his feet, took good aim at the animal, and shot it dead. The creature fell, flinging the girl headlong. She struck solidly, and lay still, in a huddled mass upon the ground. "Hurrah!" cried Frank, seeing the enemy was repulsed. "I fancy they have had about enough of us." He hastened to replenish the magazine of his rifle. Bart's first thought, on seeing the fight was over, was of the girl they had been defending. He turned and found her safe where she had been placed behind the large bowlder, but she was still holding her hands over her ears, and her face was very pale. Frank sprang outside the rocks, caught up the other girl, and leaped back quickly, placing her gently on the ground. "I hope she is not harmed," he said, as he deftly removed the mask. The moment the girl's face was exposed a shout of amazement broke from the lips of both lads. They stared first at one girl and then at the other, looking bewildered. The girls were almost counterparts of each other! "They are doubles!" exclaimed Frank. "Taken separately, it would be impossible to tell one from the other." Then he turned on the girl they had been defending, stared straight into her face for a moment, and asked: "What is your name?" "Vida Melburn." "It is not Isa Isban?" "No, sir." "Did I not change two fifty-dollar bills for you on the Pacific Express, shortly after leaving Ogden?" "I never saw you till this morning." "That settles it!" cried Frank; "the other girl is Isa Isban, and she is queen of the counterfeiters. She was the one for whom I changed the money, and she completely fooled me by her innocent face and manner." "And I mistook her for Miss Melburn," said Bart. "Such a thing seems impossible, but it actually occurred." "But how Miss Melburn came to be here is what I cannot understand," asserted Frank.