One morning, about a week after the roping of Pocut Pete, when the boy ranchers and their friends were assembled in camp, preparatory to starting out on their rounds of riding herd, Buck Tooth, who had gone to the reservoir to fish, came running down to the tents much excited. "He must have caught a big one!" commented Old Billee. But it was not fish that had aroused the old Indian. "Water stop! Water him stop all time!" he yelled. "What's that?" shouted Bud. "Isn't the pipe running?" "No run!" answered Buck Tooth briefly. "All gone!" "More trouble!" commented Bud. And then, with a grim tightening of his lips, he added: "This time we'll get to the bottom of the mystery!" There was no doubt about the fact that the water had stopped running. As they all raced up the sloping side of the reservoir they saw only a few drops trickling from the pipe. "The third time--I'm going to make it the last if it's possible," declared Bud. "What yo' aimin' t' do?" asked Old Billee. "Go through the tunnel from end to end, and both sides, and see where the water vanished to," was the answer. "We'll get up a regular expedition this time, and maybe take a boat. We'll find out what it all means." "I believe you're right," asserted Snake Purdee. "There's no use trying to work Flume Valley if the water supply is goin' to be cut off without notice. I'm with you, Bud!" "So 'm I!" shouted Yellin' Kid. "Whoop-ee! I'm a lone wolf an' this is my turn for makin' a noise! Whoopee!" "Let's find out, first, if the water is coming into the pipe from the river," suggested Nort. "You call up," begged Bud. "I'm going to get ready for this expedition. We'll have to start in the dark," he went on, referring to the black tunnel that stretched under Snake Mountain. "But we may come out into the light. Anyhow, we're going in!" CHAPTER XX INTO THE DEPTHS Preparations for exploring the mysterious tunnel on this occasion were much more complete and elaborate than when Bud, Dick and Nort walked through it before. And they did not rush off in haste, the moment it was discovered that the water no longer came through the reservoir end of the pipe line that formed the beginning and end of the old underground stream course. "There's water enough for nearly a week, anyhow," said Bud, in discussing their plans. "And if we can't discover the cause of the stoppage inside of that time, and get it turned on again, we may as well know that and give up Flume Valley as a bad job." "That's right," chimed in Nort. "The stoppage is inside the tunnel, that's sure," voiced Dick. "Yes," answered his cousin. "The water is running in all right from the river." This fact had been ascertained by telephone. The water was running freely from Pocut River above the dam, and into the pipe that entered the side of the mountain. Bud's father had been told of the situation, which followed so closely on the heels of the discovery of the evil acts of Pocut Pete.