From the rear of the plane came Jimmy’s voice. “Just what is Sub-Sahara?” * * * * * Brady’s voice went dull with routine. “Well—twenty years or more ago a labyrinth of caverns was discovered under the Sahara. It was inhabited by survivors of prehistoric Egyptians—Copts. They were trapped underground in some ancient catastrophe, and got along there, gradually growing accustomed to their environment. Matter of fact—there was a sort of colony in the old pre-dynastic days down there. The Copts worked mines, and there was a—well, a city of miners under the Sahara. When the entrance was blocked, the miners couldn’t get out—so they stayed there.” “What about food?” Jimmy asked. “And oxygen?” “There’s a lot about that Copt tribe we don’t know. Food—well, fish and mushrooms are staples. The Midnight Sea lies under the Sahara. Ages ago the water in it made the desert itself a sea, but it drained underground at last. As for oxygen, there must have been outlets before we blasted some, though they’ve never been discovered. Possibly through river caves that drain into the sea.” Captain Brady rubbed his eyes with the back of one mahogany hand. “A lot we don’t know about the Copts. Savage, ferocious—but marvelous miners. The Legion’s posted there to keep order. Prevent raids on the surface tribes. The Copts worship Isis, or the Moon—I dunno which. Probably they’re the same. Keep clear of them unless you’re armed; don’t monkey with their religion; and don’t enter any passages engraved with the emblems of the Moon and the sistrum.” “Why not?” “Religion, youngster. No white man has ever seen the Ka’aba—the Black Stone—at Mecca. It’s sacred to the Moslem, just as the Alu—the group of deepest caverns—are sacred to the Copts. They say Amon-Ra is down there.” Jimmy’s eyebrows lifted. “Amon-Ra? The ancient Egyptian god?” “Right. ‘The Hidden Light.’ We have a sort of armed truce with the Copts, provided we don’t interfere too much. When they get out of line, we whip them back. Figuratively, of course.” Brady’s hand touched the buttoned holster at his thigh. “What did you say the sacred caves were called?” Phil asked suddenly. “Alu.” “What does it mean?” “The Land of Light.” Brady looked around. His face was alight with interest. “Have you studied Egyptology?” “No—afraid not.” The captain’s eyes lost their glow. “Um. Bit of a hobby of mine. Land of Light—Hidden Light—Isis, the Moon goddess—I’ve always wondered what exists in Alu. Never found out. Never expect to. But I shouldn’t be surprised if there’s the wreckage of a civilization down there.”