Nathan looked back at the box. A cleverly arranged switch had closed when he opened the lid, exploding the thunderous charge at the mouth of the cave. He struggled mentally with the problem of who had placed the explosive and the switch to seal the cave. Perhaps Thymar had placed it as protection against robbery and his mind had been so affected by his wounds that he had forgotten it. Or someone might have planted it as a trap. But, if so, why were the Jewels left? Almost forgetting that he was sealed in the cavern, he knelt down beside the box. The inner light of the Jewels pierced his eyes and seized his mind in a hypnotic trance. For an instant he thought he was gazing upon the beauties of some fair and alien world. In the red one there was a fantastic garden of Mars, but a Mars where no red sand clouds ever covered the cities with smothering death. And in the green one he saw a fair and lovely vision of Earth so real it pierced him with nostalgia. Then the visions faded. Whether he actually saw them or they were figments of imagination he never knew. But he had to shake his head and tear his sight away from the Jewels in order to pocket them. Then, as he turned away, there broke upon the air a high-pitched song that trilled a moment's melody. It hung as if a crystal were suspended in the cavern, echoing its vibrations from chamber to chamber. It came again. Nathan straightened and put out the light. He whipped out both flame lances. It was the song of the Firebird. III Nathan darted out of the room of the Stone Pig, guided by his intimate knowledge of the cavern. He waited a moment by the entrance, listening in the darkness. Then he heard the soft scrape of a sandal against a rock somewhere. And a voice. "Nathan Ormondy!" It called his name softly, echoing in the cavern, and it was like no other voice he had ever heard. The music of its overtones was brilliant and glowing like the inner light of the Jewels of Chamar themselves. "I have come for you, Firebird," said Nathan. "Ready your flame lance." He darted away, expecting a flame to be hurled at the sound of his voice. None came. He waited, hoping Firebird would answer and give him a target. That first sound of her voice haunted him. It was the loveliness of a spring day on Earth, the blue of the sky and the song of the birds--but it was the song of the Firebird, a song of death. Then she answered. "I came to make peace, Nathan. Put up your lance and make a light." He aimed in the darkness--and could not fire at that voice. "Do you think I'm a fool?" he muttered savagely. It was to himself as well as to Firebird. "You _are_ a fool!" Firebird hissed in anger. "I came to you peacefully." From across the chamber a ball of fire the size of an orange spurted with the speed of lightning. It splattered the wall two feet from Nathan. The heat of its explosion singed his cape to a shred. His face was scorched and his eyes blinded temporarily.