One evening, as the sun was sinking, Hilary Joyce rode slowly down the old caravan road. It had a fascination for him, this narrow track, winding among the boulders and curving up the nullahs, for he remembered how in the map it had gone on and on, stretching away into the unknown heart of Africa. The countless pads of innumerable camels through many centuries had beaten it smooth, so that now, unused and deserted, it still wound away, the strangest of roads, a foot broad, and perhaps two thousand miles in length. Joyce wondered as he rode how long it was since any traveller had journeyed up it from the south, and then he raised his eyes, and there was a man coming along the path. For an instant Joyce thought that it might be one of his own men, but a second glance assured him that this could not be so. The stranger was dressed in the flowing robes of an Arab, and not in the close-fitting khaki of a soldier. He was very tall, and a high turban made him seem gigantic. He strode swiftly along, with head erect, and the bearing of a man who knows no fear. Who could he be, this formidable giant coming out of the unknown? The precursor possibly of a horde of savage spearmen. And where could he have walked from? The nearest well was a long hundred miles down the track. At any rate the frontier post of Kurkur could not afford to receive casual visitors. Hilary Joyce whisked round his horse, galloped into camp, and gave the alarm. Then, with twenty horsemen at his back, he rode out again to reconnoitre. The man was still coming on in spite of these hostile preparations. For an instant he hesitated when first he saw the cavalry, but escape was out of the question, and he advanced with the air of one who makes the best of a bad job. He made no resistance, and said nothing when the hands of two troopers clutched at his shoulders, but walked quietly between their horses into camp. Shortly afterwards the patrol came in again. There were no signs of any dervishes. The man was alone. A splendid trotting camel had been found lying dead a little way down the track. The mystery of the stranger’s arrival was explained. But why, and whence, and whither?--these were questions for which a zealous officer must find an answer.