They prepared a place to sleep for the night and alternated watches. At dawn they gathered their packs of food and water and the weapons. Firebird carefully closed the cavern over the sled. She led the way along the trail that soon rose to increasing heights above the desert. They came across the burned and blackened ruins of a sand sled, destroyed with all its equipment. "That belonged to someone who came up here for the first time as well as the last," said Firebird. "There is no love lost between searchers for the Seven Jewels. They burn each others' sleds when found." The corona lightning increased with terrible streamers of blue and violet light that twisted about the peaks like living things. The air was charged with ozone and Nathan felt the dry crackling of electric discharges in his hair and on his body. Firebird abruptly left the trails and struck out across the face of the mountain. Nathan followed and soon they came to a large overhanging rock. They slipped beneath the overhang and came into a narrow, half-enclosed passage. "Get behind me now and watch carefully," said Firebird. She turned and faced the opening under the overhang. "We may not have too long to wait." Nathan didn't quite understand, but he waited in silence. Beyond the opening, the rocks were gathered round to form a sort of small vestibule and nothing could be seen beyond that. But abruptly a man appeared in the vestibule. Firebird shot him without warning. "I just saved twenty lives," she said through thin lips. "Robert the Dog has killed five innocent men that I know of. He could have been expected to kill twenty more if he had lived ten more years." Nathan stared from the body of the dead man to the marble face of Firebird as she sat there--judge and executioner. They waited an hour and another man appeared. She killed him, too. "I've saved his mother the agony of knowing him hung for treason. The police have been ready for a month to pull him in." They waited until midday, but no one else appeared. At last Firebird turned and advanced cautiously along the passageway. Nathan felt now that killers lurked behind every stone. He didn't need Firebird's warning to keep a sharp lookout. They crept along a mile of the tortuous trail beneath the copper sky, then dipped suddenly into the blackness of a cavern. The ghostly corona that hovered over the mountain provided a faint gleam in the darkness but scarcely enough to guide them. "Take my arm," said Firebird. "I can make it in the dark." Nathan felt the tremor that was in her slight body. Some emotion beyond the grasp of his senses was surging through her. But he felt that before they left the cavern he would know what it was. After a time they came to a spiral ramp that seemed to be endless as it dropped them into the depths of the purple glow. Suddenly Firebird placed Nathan's hand on the Jewel pouch. It was faintly warm. "The buried Jewel?" Nathan whispered.