They tramped on in the blackness that was relieved only by their swaying lanterns. They walked beside the strange, underground stream, and they had progressed farther than along the other branching body of water when Old Billee, who was ahead just then, suddenly halted and uttered a warning. "Listen!" "What is it?" asked Yellin' Kid, in his usual tones, but Billee reached back and gave him such a dig in the ribs that Kid subsided with a grunt. "I hear talkin'!" whispered Billee. "Voices! There's some one else in this place than us! Listen!" They stopped and strained their sense of hearing. And then, above the slithering murmur of the water, they all distinctly heard a voice say: "I think we've fixed 'em this time! They won't steal any more water from Pocut River!" The boy ranchers looked at each other. "Del Pinzo!" whispered Nort. "As sure as Zip Foster ever ate ham and eggs!" agreed Bud. "Hush!" begged Old Billee. And as they became quiet again they heard another voice say: "I guess it's all up with 'em now. We might as well light out and touch off the fuse!" "Whew!" softly whistled Bud. Together the party of searchers moved softly forward. Suddenly the passage along the bank of the mysterious stream turned sharply, almost at a right angle. And there, in what appeared to be a small cave, excavation or cavern, high in the upper wall was disclosed a roughly circular opening, like a window or port hole. Through this port hole a light showed, and outlined in the light were several rough-appearing men, leaning together over what might have been a table. "Del Pinzo!" murmured Dick. "Conspirators!" exclaimed Bud. "They're the ones that's been turning this water on and off! We're on the track of the mystery now!" Whether he spoke loudly enough to be heard, or whether some other sound made by the searchers alarmed the men in the upper niche, was not disclosed just then. But the light suddenly went out, and confused sounds followed. And chief among these sounds was the rushing, roaring noise, the blowing as of a mighty wind, and the water near the boy ranchers and their companions was strangely agitated. CHAPTER XXIV A POWERFUL STREAM "Better look out!" came the high-pitched voice of Yellin' Kid. "There may be a flood here!" added Old Billee. "Can't we get those rascals?" cried Snake Purdee. "I'd 'a' had th' drop on 'em in another second if they hadn't doused that glim!" As he spoke they could all hear the rush of iron-nailed shoes when the wearers of them scrambled over hard rocks in their effort to escape. Mingled with that sound was the strange one of rushing water. Realizing that danger might come to them more through the agency of the strangely-acting underground stream than from the actions of the conspirators, Bud and Nort flashed their lanterns on the water-course behind them and around the bend which they had turned to behold the strange scene.