their victims a chance to free themselves. Why, why? There could be only one answer. They were waiting for something! Penrun's eyes glinted suddenly.

"Irma," he said rapidly, "we are in serious danger. The spiders have obviously put the elevating machinery of the Osprey out of commission. Helgers and his men are doomed to the Living Death as surely as though they were already lying in the silken hammocks. If the monsters choose, they could do the same thing to our sphere and doom us to the same fate. I believe they are waiting for something. While they wait we have a chance to get the treasure and escape. Shall we risk it, or shall we go while we know we are safe?"

She looked up at him evenly.

"If you think we have a fair chance to get the treasure and escape, I say let's risk it," she said firmly.

"Good!" he exclaimed. "Here we go!"

The little sphere slipped out of its cleft in the peak and dropped swiftly into the valley on the side opposite the Trap-Door City and its mysterious menace. Day was swiftly dying, and the lower passes of the mountains were already hazy with rapidly forming storm-clouds.

"Look!" cried Irma excitedly. "What are those things?"

Far in the distance a long line of wavering red lights snaked swiftly through the dusky valley toward them. Penrun picked up his binoculars.

"Spiders," he announced. "Scores of them. Each is carrying a sort of red torch. I have a feeling that those are what the monsters of the Trap-Door City have been waiting for."

He urged the sphere to swifter flight along the range. Miles from the Caves, he swept up over the peaks, and dropped down on the lowlands side. Dusk was deepening rapidly as he raced back toward the White River cataract under the pall of the gathering storm.

Among the boulders on the rough mountainside near the mouth of the Caves he eased the craft down to a gentle landing.

"Wait here," he told Irma. "I'll investigate and see if it is safe to enter the Caves."

They had seen the three men return to the ship, but others might have gone to the Caves after that. Penrun made his way down the slope to the lip of the cataract and the yawning blackness of the abysmal gorge below it.

Overhead the storm was gathering swiftly, and the saffron light of the dying day illuminated the plateau eerily. Half a mile away the Trap-Door City shimmered fantastically in the uncertain light. Penrun repressed a shudder. The Devil's own playground! Thank God, he and Irma would be out of it soon!

He crept down the narrow path that led under the ledge of the trickling cataract. Outside, a bolt of lightning stabbed down from the darkened heavens. Its lurid flash revealed the huge figure of a man, pistol in hand, beside the entrance to the Caves.

Too late to retreat now, even had he wished to. Penrun's weapon flashed first. A scream of pain and fury answered the flash, and the man's pistol clattered down on the rock. The next instant Penrun was helpless in the clutch of a mighty pair of arms that tried to squeeze the life out of him.

"Burn, me, will ye, ye dirty scum!" roared the giant of a man tightening his grip. "I'll break your damned back for ye and heave ye into the gorge!"

Penrun writhed frenziedly, trying to twist his pistol around against his enemy's back, while they struggled desperately about the ledge above the dizzy blackness of the gorge. But the pistol struck the wall beside the entrance and fell under their trampling feet.

Penrun was gasping in agony at the intolerable pain in his spine. Darting points of light danced before his eyes. Then from the opening in the rock showed a beam of white light and a man slowly emerged from the Caves. The grip on Penrun relaxed slightly as the man came toward the two combatants. Penrun could distinguish him closely now. A heavy, pasty face with liquid black eyes and a crown of thinning hair. Helgers! He was staggering and grunting under the weight of a heavy metal box.

"What's the matter, Borgain?" he asked.

"Got this bird, Penrun, we been waitin' for!"

"We don't need him, now that we already have the treasure. Still, it's a good thing we found him. Just as well to have no tales circulating about the Universe about our find. Toss him into the gorge, and go down and watch the other three chests until I get—"

"Dick, Dick!" Irma's excited voice floated down from up among the boulders. "The spiders with those red cylinder torches have arrived! They are attacking the Osprey!"

Helgers jerked up his head.

"Why, if it isn't the little spitfire!" he exclaimed in pleased astonishment. "I thought the damned spiders had eaten her long before this. Rather changes things, Borgain. I'll just go on up and let my little playmate know I am here. Toss our friend over the edge there, and bring up another treasure chest."

"What was that she was sayin' about the spiders attackin' the Osprey?" Borgain's voice was anxious.

"Oh, that's nothing the boys can't handle," said Helgers confidently. "In case they don't, we'll have to feel sorry for them and take our friend's sphere. Only have to split the treasure two ways, in that case," he added, moving up the slope.

Borgain's answer was a grunt of surprise, for his captive had squirmed suddenly out of his clutch. The big man plunged forward recklessly with arms outstretched in the groping darkness. Penrun, desperately remembering the sickening drop at their feet to the pool three thousand feet below, backed against the rock.

A flash of lightning. Borgain's ape-like arms were nearing him. Penrun lashed out at the darkened features. His knuckles bit deep into the flesh. He slipped aside as Borgain, mouthing fearful curses, rammed into the rock wall and rebounded.

Again the fumbling search. Another lightning flash. Penrun struck with frenzied desperation. Borgain took the blow behind the ear and staggered. He whirled, wild with fury, and charged vainly along the narrow ledge.

"I'll get ye this time, damn your dirty carcass—ugh!"

Guided by the sound of his voice, Penrun struck with all his strength. Borgain's nose flattened under the blow. He whirled half around.

"I'll kill ye! I'll kill—help, help—a-ah!"

Lost in the blackness he had plunged over the lip of the rock, thinking he was charging Penrun. Down into the yawning gorge his body hurtled, the sound of his frenzied, dwindling screams floating up eerily out of the black, ominous depths.

Penrun crouched against the wall, sick and trembling. Irma, Helgers! He must hurry! He fumbled again for the pistols. They were gone. Crawling forward now, still shaken by his narrow escape from death, he gained the pathway. The rain was drumming wildly on the barren granite now, and the pitch-blackness was shattered only by ghastly lightning bolts.

Guided by the flashes, he clambered up the slope and halted abruptly. The door of the space-sphere was open, and, silhouetted against the soft glow of light within it, was Irma, seated dejectedly with bowed head, heedless of the cold rain beating down upon her. Helgers was nowhere to be seen. Penrun dashed forward.

"Irma, Irma!" he cried. "What has happened? Where is he?"

She raised her head slowly and stared at him as at one risen from the dead. Then she burst into tears.

"He said they had killed you—had thrown your body into the gorge," she sobbed. "I—I just didn't want to live after that. Are you hurt?"

"Not a bit," he assured her fervently. "But where is Helgers?"

"I pistoled him," she said quietly. "I had no choice. He came at me after I warned him to keep away. He fell over there among the rocks. Oh, Dick, let us hurry away from this mad place!"

He stared at the rain-swept rocks. The heavy metal treasure chest lay a few yards away where Helgers had dropped it. Penrun moved