The sight stirred his pulse. Before him was the ancient city of the Gobi that had been the abode of a powerful race before it was invaded by the advancing sands. Past these walls the caravan of Marco Polo had journeyed. The great Venetian had spoken of a city here, where no modern explorers had found one. He had called it Pe-im. And in the ruins Mary Hastings might be still living, in desperate need of him. What interested Gray chiefly were the people of the place. He was too far to make them out clearly, and only a few were visible. This puzzled him, for Sir Lionel had mentioned a "pack of lepers." He was able to see that the people were of two kinds. One was robed in a light yellow or brown garment. Several of these men were standing or sitting on ridges outside the ruins. Gray guessed that they were sentinels. Furthermore, he believed them to be priests. The other kind wore darker dress and appeared from time to time among the ruins. They were--or seemed to be, at that distance--both men and women. The thought of the girl urged Gray to action. It would be the part of wisdom to wait until nightfall before entering the city. But he could not bring himself to delay. He was reasonably sure, from the conduct of the men acting as sentinels, that he had not been seen as yet. He had planned no course of action. What he wanted to do, now that he had an idea of the lay of the land, was to get hold of one of the men of Sungan, leper or priest, and question him about the white woman who had been taken prisoner. Mary had been in Sungan at least three days and nights. Surely the people of the place must know of her. Once Gray had an idea where she was kept, he would be able to proceed. The venture appeared almost hopeless. How could he enter the ruins, find the girl, and bring her out safely? What would they do then? How was he to deal with the lepers, whose touch meant possible contagion? But he was hungry for sight of Mary--to know if she was still alive. He could not wait until night to learn this. He marked the position of the nearest men in his mind, returned the glasses to their case, loosened his automatic in its sheath, and slipped down from his lookout behind the ridge. "I've cut out sentries," he mused grimly, "but not this kind. They don't seem to be armed." In fact, the men of Sungan were not armed--with modern weapons. But they had a deadly means of defense in the disease which bore a miserable death in its touch. Gray, for once, blessed the continuous dunes of the Gobi. He went forward cautiously, keeping behind the ridges and edging his way from gully to gully, crawling at times and not daring to lift his head for another look at the sentinels he had located. His sense of direction was good. He had crawled for the last half hour and the sun was well past mid-day when he heard voices a short distance ahead.