Art chuckled at the Martian's audacity. The sounds of pursuit were getting fainter behind them. The Voornizar were learning new respect for their once despised captives. The tunnel now narrowed down to a width which made it passable by one person only, and ran perfectly straight. The party formed in single file, Klalmar-lan bringing up the rear. Denny led, with Art's flash, as Art was nursing scorched hands and arms. "They'll be getting after us with that paralysis ray directly," Art worried. "What do you say to blocking the tunnel? We can surely depend on its emerging somewhere." "The War Gods help us if _they_ know where it comes out! But I think you've got an idea there," agreed Klalmar-lan, turning his ray on the roof of the tunnel a good distance behind them. It crumbled, slowly at first, then gave way with a roar, the fragments of rock and masonry completely choking the aperture. Klalmar-lan did not stop until he had filled the passage for a good hundred feet. "We can get back through there, if we have to, by using this gun, but the Voornizar will have to dig or bore their way. Their disintegrators are like yours of Earth--uncontrolled. They are useful out in space for destroying an enemy space ship at a distance, but one blast under ground here would set off enough thermal energy to blow this whole city off the green face of Venus." * * * * * Denny was crouching on the floor. "Look at this!" he exclaimed. His tiny flash revealed fresh marks in the damp sand which covered the floor at that point. They were blurred, and had no resemblance to human footprints. "At least one Voornizar passed this way," commented Klalmar-lan, "but my guess is that Dwalbuth made these tracks, and was the only one who knew the secret of this passage." "It's a sure thing it's leading us to some place of importance--Dwalbuth didn't take this walk for the fresh air," Denny contributed. The tunnel's length seemed interminable, although Art estimated they had not covered over four or five Earth miles. They found a tiny spring of pure water trickling down the moss-shrouded stone wall, and drank gratefully. Their lunch consisted of a few food tablets which Art had been carrying. At last a dim glow of light appeared ahead. Advancing warily, they found the passage ran squarely into a plate metal barrier, which leaned away from them at a slight angle. About head height, there was a small ragged hole burned into it, through which came the light they had seen. Denny applied his eyes to this.