Had there been natural water-holes in Flume Valley it would, long ago, have been used as a place to raise cattle. But it was the absence of drinking places that caused it to be passed by, until, by artificial means, tapping the river through the underground course, Mr. Merkel had enabled his son and nephews to become boy ranchers in earnest. As Bud had stated, there was about a week's supply on reserve in the concrete reservoir. When that was exhausted, unless the water again started flowing through the pipe, the cattle would suffer from thirst. "Well, she isn't spouting any," mournfully remarked Nort, as, with his brother and Bud, he ascended the slope, standing on the edge of the reservoir. "No," agreed Bud. "She's as dry as an old buffalo skull now. I don't know what to do!" The shadows of dusk were falling, and the boys felt that the night was coming with its gloom to match their own feelings. Failure seemed to stare them in the face. "But I don't see how anyone--granting that somebody like Hank Fisher or Del Pinzo has it in for us--can shut off the water without operating at either end of the flume!" exclaimed Nort. "That is queer," agreed Bud. "I wonder what's inside that tunnel where the old watercourse runs? I've been through it, but couldn't see much of anything. I've a good notion----" He broke off his remarks to gaze intently ahead. There was a movement in the gloom, and a figure walked away. "Who's there?" asked Bud sharply, his hand slipping to his .45. "It's me," came quickly, if not grammatically, from Pocut Pete, whose voice the boys recognized. "I just moseyed up here t' see if she was runnin'." "Well, she isn't," spoke Bud, a bit shortly. "So I see," came the drawling answer, and it was followed by a faint tinkling of glass. Bud started, and tried to pierce the night shadows. But all he saw was the figure of the strange cowboy becoming more and more indistinct. Bud was just going to say something when he was halted by the voice of Nort. "I have an idea!" exclaimed the eastern lad. "What is it?" asked his brother. "Anything to do with this?" and he waved toward the reservoir which was strangely still, now that the water no longer bubbled into it from the pipe. "Yes," went on Nort. "Why not investigate and see where the stoppage is, Bud?" "Investigate what?" "The pipe line--the old underground water-course." "You mean go through the tunnel?" Bud asked. "Sure! Why not? You say it's big enough all the way through, and the water itself doesn't occupy much of the bottom. We could walk it in a day, easy!" "Yes," agreed Bud, "it isn't more than five miles, though we'd have to carry lanterns, and we might get lost in some side passage." "That's just what I want to find out about!" cried Nort. "If there _is_ a branch passage maybe that's where the water goes! Come on, Bud, let's go through the tunnel!" "I'm with you!" said Dick.