"I know now! This is where we got in that fight with the hidden gunman! And over there ought to be--sure enough! The water hole! I didn't think we were so near it. I must have come further than I thought. Well--might as well take a look around. Right here is where the bird that did all the shooting must have lain. Come here, bronc!" The boy dismounted and slipped his horse's bridle rein on his wrist. Then he threw himself down on the sand in the position their antagonist might have taken when he fired at them. "Here I am with a view of the water hole, and in a good place to shoot from without being shot. Now I want to get away quick. What do I do? If I roll to the left, I expose myself to fire. If I roll to the right, I--" there was a little clump of mesquite by his right elbow. Bud pulled himself toward this. "That would afford protection, but once I get in here how can I get out? Now--" The boy was rolling to the center. With a "Hold it, bronc!" he released the reins and his hand slid off the clump. Suddenly a queer thing happened. Bud felt the ground below him give way, and the next moment he found himself in a hole just large enough to admit his body, and about four feet deep. Above him the bushes had closed again, effectively screening him from the view of anyone above ground. He had accidentally solved the mystery of the gunman's strange disappearance. For a few seconds Bud lay still, so sudden was the shock of the fall. He was not really stunned, however, and as soon as he recovered from his surprise he struggled to his feet and parted the brush above him. His horse was near by, moving slowly and cropping grass. Then he saw how easily it would be to escape observation by falling into the small pit. The bush was certainly not large enough to conceal a man, and for this reason no one would imagine it could serve to screen a hole. It afforded a perfect hiding place. On either side was flat prairie, and no one would suspect the presence of a hidden person in that country. "So that's how it all happened!" Bud gave a low whistle. "No wonder we missed the fellow. Say, this is one bird of a hiding place! All a man has to do is to roll in it, like I did. Anyone who can tell this hole is here without being in it is a better detective than I am. "But what a crazy spot for a hiding place! Surely whoever dug it didn't know he'd use it to fire on us and then escape. Must have been some other reason for making it, and then it came in handy when whoever shot at us wanted to get away. He must have just lain quiet while we looked around, then, when we left, he just came out and walked away. Clever, all right. Now who'd think of a stunt like that?"