He had pulled his horse up with a swift tightening of his hand. Now the beast stood with head erect, and pricked ears firmly thrust forward. Its head was turned southward, and the gush of its distended nostrils warned its rider that his question was shared by a creature whose instincts were even more acute, here, on the prairie, than those of its human master. Bob bent down in the saddle the better to obtain the silhouette of the sky-line. The sound which had held him came up on the southern night breeze. It was a low murmur, or rumble, and, to his accustomed ears, it suggested the speeding of hoofs over the green clad earth. He waited for many moments, but the sound only increased. There was no doubt left in his mind now. None at all. He sat up again and glanced swiftly about him. The moonlight had increased, and a silver sheen threw up the surrounding scene into indistinct relief. Beyond, to his right, he detected a small patch of scrub and spruce, and, without a second thought, he made for it. A minute later he was out of the saddle beside his horse, screened from view of the plains by a belt of bush. He secured his horse and moved to the fringe of his shelter. Here he took up a position facing south, and his view of the plains beyond became uninterrupted. He knew what was coming. Instinct warned him. Perhaps even it was the wish fathering his belief. He felt it was a certainty that the rustlers were out pursuing their depredations with their customary unchallenged daring. Who, he wondered, was the present victim, and what was the extent of the raid? He had not long to wait. The sound grew. It lost its distant continuity and became broken into the distinct hoof beats of large numbers. Furthermore, by the sound of it, they would pass right across his front. He had been wise in seeking cover. Had he remained---- But speculation gave way before the interest of movement. Now the silhouette of the sky-line was dancing before his eyes. In the moonlight he could clearly make out the passing of a driven herd. It came on, losing itself in the shadows of a distant trough. Again it appeared. More distinct now. He whistled under his breath. They were coming from the direction of Dug McFarlane's and it was a large herd. They were traveling northwest, which would cut into the hills away to the north of his homestead. They---- But they were almost abreast of him now, and he heard the voices of men urging and cursing. Lower he dropped toward the earth the better to ascertain the numbers. But his estimate was uncertain. There were moments when the herd looked very large. There were moments when it looked less. He felt that a conservative estimate would be one hundred perhaps, and some eight or ten men driving them.