"Ain't fer human understandin'," one superstitious miner whispered in awed tones. "Twenty year I bin on this cursed planet--nor ever heerd the like o' this." "It's clear enough for me," answered a pink-cheeked youngster up to Mars to make a fortune in rich ore dust. "I stay off the desert at night. Only the miserable Martians can live out there then." "Justice from the Crypt," a third muttered, quoting the threat of an old Martian, dying from wounds he'd received fighting Earthmen. "It's like from the grave--this mist, the way it creeps from the sand white and ghosty!" That was the spirit Barry Williams, special investigator for the Terrestrial Bureau of Martian Affairs, found when he arrived. Behind the fear were rumors, dead bodies, nothing more. At first, he'd blamed superstition and the natural hazards of work in the desert. But now he was here in the desert at night, waiting. * * * * * It wasn't for this he'd been sent to Mars, Barry told himself half-angrily. His mission here was important. But this threat to all Terrestrials on Mars was ominous. There were no government agencies to deal with the threat here. Mars was just a frontier where untold riches lay for the taking beneath some of the red sand. The sullen, cowed Martians, working at the bigger mines, or following their nomadic courses across the desert no longer attempted an organized government. Despite their great majority in numbers, the Martians played no part in running the planet. How they must be rejoicing now, Barry thought, as death stalked their conquerors, death striking from the desert in the night. Suddenly, Williams felt an icy tingle course through his blood. His hand dropped again to his ray gun, tore it from the holster. He stood erect, fighting an urge to crouch low against the danger. Along the crest of the sand-swell before him, something was rising. Bright moonlight shimmered as the rays broke against a pale barrier. To the right, the left, behind him, it was the same. The white mist was rising, surrounding him. Escape was cut off. Even to reach his nearby spaceship was impossible without cutting through. Barry tried to relax. There was nothing to do but wait. He remembered the words of the old Martian desert wanderer to whom he'd spoken. This man had once been a chieftain, before the conquest of Mars by Earth. His keen black eyes had bored into Barry. "If you wish the answer," he'd advised, "go into the desert at night. _You_ are different--_you_ may return. I can tell you no more." Thicker grew the mist. A silver blanket, wrapping closer and closer about Barry Williams. The moons and the barren landscape were blotted out. All perspective vanished. High above, a tiny patch of stars was visible--perhaps for the last time to Williams.