"Yes, on scout, or detached duty," was the answer. "The government has had many complaints of this band of Del Pinzo's rustlers, and we were detailed to put them out of business. I was assigned to go on duty as a cowboy, which wasn't so hard, as I had been one nearly all my life before joining the army. I worked on several ranches, picking up bits of information here and there, and I completed all I needed to get in Happy Valley," he added. "And we never tumbled!" remarked Dick. "Glad you didn't!" laughed Lieutenant Wayne, to give him his proper title. "I thought you were suspicious of me, more than once, though," he said. "We were, after you built that signal lantern on the watch tower--you did do that, didn't you?" asked Bud. "Yes, but only as a decoy for the rustlers. I managed to overhear some of their plans, and part of their scheme called for a light on the tower when the time was ripe for a raid on your cattle, boys. So I flashed the signal myself, and, indirectly, it led to this capture today. For I joined my troop right after that, and we have been rounding the rascals up ever since. "We knew they had made a big raid at your place, but we didn't know where they had hidden the cattle until I happened to think of this old crater, which I discovered one day when I was working for you, Bud. So we made our way here and--well, this is the end, I believe," he added, as he looked over at the bunch of miserable prisoners. "I hope it's the end," said Bud. "We want to get back to business. And I'm sorry we suspected you, Lieutenant." "Oh, that's all right. In fact, I'm glad you did. It shows I lived up to the character I was supposed to represent." There is little more to tell. That night, around the campfire many things, hitherto a mystery, were explained. The stethoscope the boys found was the property of Lieutenant Wayne. He had dropped it when paying a secret visit to Happy Valley. He had intended to pose as a doctor to deceive the rustlers, but, on losing the stethoscope he gave up that plan. It is needless to say that he had nothing to do with the robbery at Diamond X, the real thieves never being discovered. Lieutenant Wayne apologized for cutting his way from Bud's tent the night he disappeared after the signal from the tower. This was the only way he could disappear and accomplish his plans, he said. And it was he who had fired and broken the bottle, and had also fired mysterious signal shots, in order to play up to his character of being in with the rustlers. "Though the bottle-breaking was only a joke I indulged in," he admitted, "I'm sorry it worried you so." The soldier, of course, had nothing to do with the prairie fire, and who set it, if it was set, was not discovered. Lieutenant Wayne finally recovered his black horse Cinder, the animal having made its way back to Curly Q ranch, where the officer once posed as a cowboy.