Ralph strained his eyes into the darkness, but could see nothing of the object Jack had indicated. It had gone as utterly as if it had not been there.
Suddenly the wild howls that had awakened Ralph broke out once more. This time they came quite close at hand, and neither boy could repress a start at the sound. It gave an impression of an outburst of demoniac mirth.
"Wow! ow-ow-ow-ow-ow!"
The cry was immediately echoed from the direction in which Jack had declared he had seen a gray shadow flitting in and out. The next instant both boys gave an involuntary shout of surprise, which they hastily checked, realizing that they were face to face with a stern necessity for silence.
Outlined as clearly against the moonlight as if it had been cut from black paper, the figure of a horseman had momentarily appeared, and then as abruptly vanished.
At the same instant there came a wild disturbance of hoofs in the corral, and before the boys' astonished eyes four more horsemen dashed from it and swept off toward the south. Behind them there trailed half a dozen of the animals which had been feeding or sleeping in the corral. To the neck of each was attached a lariat, and they followed their captors at breakneck speed.
"Horse thieves!" shouted Jack, springing to his feet and giving the alarm by firing a volley of bullets after the retreating rustlers.
Instantly the sleeping ranch galvanized into active life. Lights flashed here and there, and from the bunkhouse on a hillside below the main house there poured a strangely assorted score of hastily aroused cowboys. Some of them were trouserless, but all carried their revolvers.
"What's the matter? What is it?" shouted Mr. Merrill's voice.
"Dad, it's horse thieves!" shouted Jack.