The Earthman fired at the monster. The first bullet clinked harmlessly on his opponent's breast-plate. The second thudded full force upon its skull, but apparently the hard smooth skin of the creature was too tough to allow projectiles hurled from a pistol to penetrate it for it did no real damage--only infuriated the monster. Black hard lids dropped protectingly over its eyes, and its mouth worked convulsively. It quickened its pace and brought its own pistol into play. Shelby had made a hasty survey of the hall and had noted the stairway beside the door he had tried to open. He darted up this, ducking low behind the stone railing to avoid his weird pursuer's bullets. Perhaps in the chambers above he could find a means of escape. He was leaving a trail of blood on the marble steps, and his wound pained him terribly. He felt sick and weak. When he had reached the top of the stairs, the unknown horror was already halfway up. It had returned its pistol to its holster. Apparently it had been so maddened by Shelby's shots, that only tearing its quarry to pieces could satisfy its lust for vengeance. And the thing was gaining rapidly! But the Earthman gritted his teeth and kept doggedly on. He fought back the nauseous giddiness that was creeping upon him. He'd have to escape. Oh God! There was too much at stake--the world and Jan--what was happening to Jan? True, he had killed Selba, but certainly the Martian had minions--men who could carry on without him. He could scarcely have built up all his plans single-handed! Four flights of steps Shelby and his pursuer ascended. Was there a way of reaching the roof and the plane in this direction? And if there were, could the Earthman reach it before the long arms of the thing so close behind wrapped themselves about him? Such an event, Shelby knew could not mean anything less than failure, and possibly immediate death. The fiend behind did not cry out or order him to halt. In fact it made no vocal sound at all. Not even its breathing, which should have been heavy and labored, was audible. Only the hurried shuffle of its unshod feet. Its silent relentlessness was nerve-wracking. The engineer saw before him at the top of the stair a small doorway, and beyond it a spiral runway leading upward. The light grillwork gate stood invitingly open. Catching the grill with one hand as he rushed through the door, Shelby sought to slam it shut and latch it. He almost had succeeded, and then a huge hand closed upon the bars. One jerk, and a quick grab with the other immense paw and the strange flight and pursuit would be at an end. But the jerk was delayed. Shelby fired his last round. It did the monster little harm, even though the distance between the two was but four feet. Nevertheless it caused the armored horror to leap back a step, and the moment thus provided was sufficient.