In the station they mingled with farmers, miners and homesteaders. Couples such as themselves were common on Mars; they were going out to make their fortunes. They bought their tickets to Port Karnak. Ed and Barbara looked around them. A half-dozen men among the waiting passengers wore no oxygen helmets. True, this underground depot was pressurized, but the outer thinness and oxygen-poverty of the Martian air had to be prepared for. The absence of helmets, then, almost had to be the mark of the android. To keep its vital processes going, the versatile vigor of vitaplasm merely disintegrated a tiny bit of its atomic substance, to make up for the shortage of chemical energy. Ed and Barbara boarded the train with the crowd. Much of this underground system of transportation had merely been converted to human beings' use from that which had remained from the ancient culture of Mars. Behind the projectilelike coaches, close fitting in the tubes, air-pressure built up. Acceleration was swift. Covering the thousand-mile distance to Port Karnak took twenty minutes. Once arrived, Ed bought the additional equipment they needed; then in a small restaurant they ate a last civilized meal. They took an auto bus out along a glassed-in, pressurized causeway and descended at the final stop, beside a few scattered greenhouses, the outermost of which provided the city with fresh, earthly vegetables. Here the desert was at hand, utterly frigid at night, under the splinters of stars. Deimos, the farther moon, hung almost stationary in the north. Irregular in shape, it looked like a speck of broken chinaware, just big enough to make its form discernible. Probably it was a small asteroid which the gravity of Mars had captured. The Dukases began to plod. The desert came under their boots, and the solidity of the ground gave way, gradually, to a difficult fluffiness, like that of dry flour. It was millions of square miles of dust the color of rusted iron, which, in part, it was. Dust, ground to ultimate fineness by eons of thin, swift wind. Under the dim light of the sky, colors dropped in tone to a monotonous grayness that only faintly revealed the nearest dunes, and showed plumes of soil moving on the wind like ghosts. The dust made a constant, sleepy soughing against their helmets, like an invitation to death. Barbara pressed Ed's gloved hand, as if in reassurance, and he pressed hers in return. Maybe they had eluded all pursuit or probe-beam tracking. Certainly the blowing dust itself would be an effective screen against the most refined radar device. Yet to vanish from the view of men could mean another kind of danger. It came to Ed that even when Mars had teemed with millions of its own inhabitants, perhaps no one had trod within a mile of where he and his wife were now walking.