“There’s the fort. Over there—” He pointed. “That’s the entrance to the Coptic tunnels. We guard the entrance to the surface. Though the Copts haven’t tried to make any surface raids for a long time.” He swung out along a rough path, the others following. “They hate the Bedouins, just as the ancient Egyptians did. They don’t especially dislike us, unless we get in their way. If the mineral deposits the Copts work weren’t valuable, though, they’d be left to themselves. But the Legion’s paid to make sure the mines are kept active.” Tony didn’t answer. His eyes were slowly accustoming themselves to this strange light. He glanced up at a ceiling that was both visible and invisible. No details could be seen. A veil of shining cloud seemed to obscure the rock far above. The vault of a world, Tony thought. A world created here, perhaps, when the Sahara was a sea instead of a desert. What had Brady said a while ago? Something about a prehistoric, mighty civilization in ante-dynastic Egypt ... and, far and far below, the Copts still worshiped Isis, in the hidden caverns of Alu where no white man had ever penetrated. “The wreckage of a civilization down there,” Brady had said. In this eery cavern-world it was easy to believe in almost anything. A scrap of half-forgotten verse drifted through Tony’s mind: “_But you have seen the hieroglyphs on the great sandstone obelisks,_ _And you have talked with Basilisks, and you have walked with hippogriffs_ ...” They were at the fort. Nothing could be seen beyond a palisade of strong, dully-gleaming metal. But a bell rang sharply; a gate opened, and a man in legionnaire uniform appeared. Even in the odd light his face seemed strangely pallid—drained of all color, like bleached papyrus. He was gaunt and fleshless almost to the point of emaciation, so that his eyes and mouth were black hollows. It seemed as though a skull wore the rakish Legion cap atop its dome. He saluted, and Brady responded. “Hello, Jacklyn. Tell Commander Desquer I’m here.” * * * * * Jacklyn stood aside to let the others enter. Tony discovered that within the palisade were a dozen metal shacks, prefabricated, and without sign of life. So this would be their home from now on! Brady said, “Well? Didn’t you—” Jacklyn’s voice was strained. “Glad you’re back, sir. The commander left for the surface an hour ago. He got a message.... There’s trouble, sir. The Copts—they’ve kidnapped Ruggiero.” Captain Brady looked at his fingernails. “It’s full moon, isn’t it?” “Yes, sir.” “All right. I need four men. Completely armed. We’ll leave as soon as they’re ready.” Jacklyn hurried away. Tony asked, “Is this—the usual thing, down here?” Brady shook his head. “No. At full moon the Copts choose a victim to represent Osiris. The Husband of Isis. Usually it’s all done quietly, and the sacrifice is a Copt, of course.” Jimmy inquired rather weakly, “What sort of sacrifice is it?”