The march Royson had undertaken was a trying one. The desert runs to extremes, and, at that season, the thermometer varied a hundred degrees between noon and midnight. When the sun dipped behind the hills, a tense darkness fell on the land. This impenetrable pall is peculiar to Egypt; probably it suggested to Moses that ninth plague wherewith he afflicted the subjects of a stubborn Pharaoh. Though this "darkness that may be felt" yields, as a rule, to the brilliancy of the stars after half an hour's duration, while it lasts a lighted match cannot be seen beyond a distance of ten or twelve feet. It is due, in all likelihood, to the rapid radiation of surface heat. When the cold air has robbed sand and rock of the temperature acquired from the broiling sun, the atmosphere clears, and the desert reveals itself again in the gloomy monotone of night. It may reasonably be supposed, that the excess of humidity which caused the remarkable mirage of the afternoon helped to continue the "black hour," as the Arabs term it, far beyond its ordinary limits. Hence it was nearly ten o'clock when Royson quitted the camp on his self-imposed task. To all outward semblance, he differed not a jot from the two Arabs who accompanied him. A burnous and hood covered his khaki riding costume. He bestrode a powerful camel nearly eight feet high. Like his companions, he carried a slung rifle; a haversack and water-bottle completed his equipment. His size alone distinguished him from Abdur Kad'r and Sheikh Hussain of Kenneh, the latter being a man whom Abdur Kad'r had selected as best fitted to win his way unquestioned into the Italian camp. Royson's Arab dress was intended to secure the party from espionage while they traveled towards Suleiman's Well. When they neared it he would throw aside the burnous. His pith helmet was on his saddle, but the Arab hood enabled him to dispense with it by night. The older Arab led: behind him rode Royson; Hussain brought up the rear. In this fashion they climbed the slight rise of the wide valley which sheltered the expedition. They had gone some three hundred yards, and the leader was scanning the horizon for a gap through which the track passed, when they were all amazed to hear Miss Fenshawe's clear voice. "I thought you were never coming, Mr. Royson," she said. "I was on the point of going back to my tent, but I caught the grumbling of your camels. Then I knew that you had really made a start." After the first gasp of wonder and delight, Dick slipped to the ground. He narrowly avoided a spiteful bite from his unwilling conveyance, but he handed the single rein to Abdur Kad'r, and hastened towards a rock in whose shadow stood Irene, garbed and cloaked so that she was scarcely discernible. "I cannot tell you how glad I am to see you, Miss Fenshawe," he cried, "yet, in the same breath, I must protest against your wandering so far from the camp. Are you alone?"