Finally, he came to the ninth wheel. His excitement was now so great that those in the gallery could see that he was trembling violently in every limb.
He troubled no longer with the Sunstone. He turned the wheel very slowly, with his eyes fixed upon the red granite rock. Presently there was a "click" like the sound of the turning of an enormous lock. Captain von Hardenberg held the wheel quite still.
There came another "click" even louder than that which had gone before. And then slowly, like some great living monster, the rock began to turn, as if it revolved upon a pivot.
It turned evenly, slowly, noiselessly, and, as it turned, the light from the lamp caused the quartz and mica and felspar in the granite to glisten like a thousand fire-flies on a summer's evening.
And then, in the moving rock itself, appeared a narrow archway about four feet across; and when this was immediately opposite the altar there was another "click" and the whole rock was still.
Those in the gallery sprang to their feet and looked on with bated breath. The thing was like a miracle. As for von Hardenberg, he gave vent to a cry that was half a cheer and half a sob. Then, snatching the lamp from the altar, he rushed through the archway into the darkness beyond.
From the gallery they could see the light grow smaller and fainter as the Prussian descended a narrow flight of steps. Then the light went out, and there came up from the vault beyond a faint cry of exultation. Captain von Hardenberg had attained the treasure of Zoroaster.
And it was at that cry that the Black Dog glided from his hiding-place. Now that the lamp had gone, the cave was darker than before. But by the light that came from above, and through the entrance, those in the gallery could see his white robes as the man glided noiselessly across the hall.
He went straight to the altar, picked up the Sunstone, raised it to his lips, and kissed it. For a moment he gazed at it, long and lovingly, before he thrust it into a pocket.
He moved on tiptoe towards the wheels. As he did so he passed through one of the shafts of light, and his features were illumined. On his face there was an expression that was diabolical. It was the face of a beast of prey, a tiger that stalks its victims. His white robes contrasted strangely with the swarthiness of his countenance. His eyes were very bright and now looked yellow like those of a cat.