"Why, bless me, boys, what can it mean?" he cried, nimbly attempting a flying leap over the edge of the altar in his haste to ascertain for himself the nature of the approaching party. Suddenly, however, as his feet touched the top, and he was scrambling over, he gave a sharp cry and fell back within the altar with a gasp of pain. "Are you hurt?" asked Jack, running to the side of the ancient place of sacrifice. The professor lay prostrate within. His face was white and set and beads of sweat stood out on his forehead. "My--my ankle," he groaned. "I broke it some time ago, and in hurrying to clamber over the top of the altar I fear I have snapped it again. Oh!" He gave a heartrending groan of pain. The boys stood stricken with consternation. It was going to be a long and difficult task to get the professor out of his present predicament, and there seemed need for haste. "Here, put this under your head," said Jack, stripping off his jacket hastily, and throwing it within, "I'll tell Coyote Pete about your accident, and we can get remedies from the packs." But when Jack turned, only Ralph and Walt stood beside him. The sturdy cow-puncher had vanished. "He's gone to get the glasses," explained Walt. Presently Coyote Pete, very much out of breath from his dash down the path and up again, stood beside them. He had the glasses in his hand, and lost no time in applying them to his eyes. He had not had them there two minutes when he gave a quick exclamation and turned hastily to the boys. "Lie down; lie down, every one of you," he ordered sharply. They lost no time in obeying, as they knew that the old plainsman must have an excellent reason for such a command. The next instant Pete himself followed their example. Crouching low, he once more peered through the glasses above the edge of the cup-like depression. "Who are they?" asked Jack in a low voice, wriggling his way to Pete's side. "I'm not sure yet, but they are all armed. I caught the flash of sunlight on their rifles. If they are Mexican insurrectos, we are in a bad fix." "Mexicans! What would they be doing this side of the border?" "That remains to be seen. But I don't like the looks of it." "Suppose they are Mexicans, Pete, would they do us any harm?" "That depends a whole lot on whether they are on lawful business or not." "You mean----" "That I don't like the looks of it. If there's an insurrection in Mexico, those fellows are after no good on this side of the border. They may be some band of cut-throats, who are taking advantage of the disturbances to raise Cain." "Good gracious," exclaimed Jack, "and the professor's just injured himself so that we can't move him for some time anyhow." Coyote Pete turned sharply on the boy. "What's he done?" "Broken his ankle, or, at any rate, seriously sprained it."