One sharp, short order from Hervey stopped the foremost as they ran for the entrance. In fact, not one of them was peculiarly keen to follow such a trail as this in the darkness. Breathless silence fell over the patio, and then they heard the departing beat of the hoofs of Red's horse. And the shock of every footfall struck home in the heart of Marianne and filled her with a great loneliness and terror. And then the noise of the gallop died away in the far-off night. CHAPTER XVII INVISIBLE DANGER Alcatraz, cresting the hill, warned the mares with a snort. One by one the bays brought up their beautiful heads to attention but the grey, as was her custom in moments of crisis or indecision, trotted forward to the side of the leader and glanced over the rolling lands below. Her decision was instant and decisive. She shook her head and turning to the side, she started down the left slope at a trot. Alcatraz called her back with another snort. He knew, as well as she did, the meaning of that faint odor on the east wind: it was man, unmistakably the great enemy; but during five days that scent had hung steadily here and yet, over all the miles which he could survey there was no sign of a man nor any places where man could be concealed. There was not a tree; there was not a fallen log; there was not a stump; there was not a rock of such respectable dimensions that even a rabbit would dare to seek shelter behind it. Still, mysteriously, the scent of man was there. Alcatraz stamped with impatience and when the grey whinnied he merely shook his head angrily in answer. It irritated him to have her always right, always cautious, and besides he felt somewhat shamed by the necessity of using her as a court of last appeal. To be sure, he was a keener judge of the sights and scents of the mountain desert than any of the half-bred mares but though he lived to fifty years he would never approach the stored wisdom, the uncanny acuteness of eye, ear, and nostril of the wild grey. Her view-point seemed, at times, that of the high-sailing buzzards, for she guessed, miles and miles away, what water-holes were dry and what "tanks" brimmed with water; what trails were broken by landslides since they had last been travelled and where new trails might be found or made; when it was wise to seek shelter because a sand-storm was brewing; where the grass grew thickest and most succulent on far-off hillsides; and so on and on the treasury of her knowledge could be delved in inexhaustibly. On only one point did he feel that his cleverness might rival hers and that point was the most important of all--man the Great Destroyer. She knew him only from a distance whereas had not Alcatraz breathed that dreaded scent close at hand? Had he not on one unforgetable occasion felt the soft flesh turn to pulp beneath his stamping feet, and heard the breaking of bones? His nostrils distended at the memory and again he searched the lowlands.