One by one the cowboys drifted in, some singing ranch songs in spite of their weariness. Bud and his cousins were through with their meal first, and, having persuaded his sister, Nell, to pack a basket of doughnuts, pie and cheese for him, Bud signalled to his cousins to join him out at the pony corral. "Let's get an early start back to Happy Valley," he urged. "It's a long enough ride, anyhow." "You said it!" commented Nort. "Well, there's one thing we don't have to worry about, and that is not finding any water running into the reservoir," added Dick, as he slipped in through the gate and caught one of his ponies--not Blackie, who was tired out from the round-up. Each cow puncher, including the boy ranchers, had several animals in his "string." "No, I guess, since we solved the mystery of the water supply, we'll have no more trouble," agreed Bud. The boy ranchers rode over the trail to their own camp--it was actually a camp, for permanent ranch buildings had not yet been erected in Happy Valley, though some were projected. Tents formed the abiding place of our heroes, and as they were only there during the summer months the canvas shelters served very well, indeed. The moon rose, shining down from a starlit sky, as the rough but faithful and sturdy cow ponies ambled along. Now the boy ranchers would be down in some swale, or valley, and again topping one of the foothills which led to Buffalo Ridge or Snake Mountain, between which elevations lay Happy Valley, where the cattle of Diamond X Second were quartered. "There she is--the old camp," murmured Dick, as they started down the slope which led to the collection of tents erected against the earthen and stone bank of the reservoir. "And maybe I won't hit the hay!" exclaimed Bud, with a yawn. "We don't have to get up to-morrow until we're ready." "Oh, boy!" cried Nort in delight. They rode forward, and were almost at their camp when Bud, who had trotted ahead, pulled his pony to a sudden stop and cried out: "Hold on there! Who are you and where are you going?" At the same moment his cousins saw the moon gleaming on the .45 gun which Bud drew from his holster. CHAPTER II A CURIOUS INSTRUMENT "What's the matter, Bud?" asked Dick, as he urged his animal forward in a jump, until he was beside his cousin. "Some one's up there around the tunnel entrance," responded Bud Merkel. "I saw 'em dodge back out of the light." Then, raising his voice, he cried: "Come on, now! None of your tricks! I've got you covered!" "I don't see any one," spoke Nort. "They're there, all right," asserted Bud. "Come on, fellows," he exclaimed, "we'll have to look into this. There was trouble enough with getting water to stay in Happy Valley, without letting some Greaser in to queer the works again! Come on!"