"Why, the Commander, naturally--assisted by myself." Luhor's vast chest arched with pride. "Observe closely, Earthman, and you will be treated to as masterly a feat of navigation as you're likely ever to see again!" His purple orbs roved over the men, clean-dressed, and rested, the haunted look beginning to fade from their eyes. He nodded approval, as he turned and left. "A base at Vulcan!" Mark was repeating inwardly. And a cold fear at this growing mystery grew apace within him. It was not only a masterly feat of navigation--it was incredible as the hurtling spaceship continued along its tangent, until Vulcan, slightly smaller than Mercury, came swinging around to bisect their trajectory. Very neatly, their speed was manipulated to allow the planet to come between them and the sun; then the great Spacer began to pursue a direct course. Mark noticed that Vulcan kept one side eternally sunwards. Swiftly the spaceship approached the dark, outward side. Actually it was not "dark" but it could be called so in comparison with the molten sunward side. Mark realized the almost insurmountable difficulty of keeping the Spacer on a trajectory, with the sun's tremendous gravitational pull so dangerously near; the slightest deviation now would send them hurtling past Vulcan and into that naming hecotomb. He knew, as well, that there could be no atmosphere on Vulcan to help them brake. * * * * * But even as these thoughts were racing through his mind, Vulcan came rushing up at them with the fury of a miniature hell running rampant. Its surface was lividly aglow, with the flaming curve of the sun as a backdrop blotting out the horizon. Suddenly they were leveling over its surface, at a speed that to Mark spelled disaster. He saw the fore-jets flaming over a wide terrain of what might have been lava or pumice, but that didn't seem to check their reckless speed at all. Directly ahead black mountain ranges sheered upward as if to disembowel the ship on jagged summits. Mark merely closed his eyes, awaiting the crash that seemed inevitable. No ship he knew could ever brake in time at that suicidal speed. A terrific force jarred him to the floor. A profound nausea made him retch. Then Luhor was touching his shoulder, and Mark opened his eyes. "All out, we're home!" the half-breed grinned. "You're lucky that the synchronized magnetic fields minimize deceleration, Earthman." Doors were opening, voices were drifting into the ship. The vibration of the atomomotors had ceased. White-faced and shaken, the men debarked into a wide corridor hewn out of solid rock, into which the ship had berthed. Glancing back, Mark saw metal doors of titanic proportions now hermetically closed; ahead were similar doors. Then he heard the deep, far-away throbbing of generators and he knew that he was in an air-lock built on a gigantic scale. A few seconds later the inner doors slid open.