Feeling his way along the narrow ledge, Bradley came presently to a blank wall that stretched out over the water swirling beneath him, as far as he could reach. Stooping, he groped about with one hand, reaching down toward the surface of the water, and discovered that the bottom of the wall arched above the stream. How much space there was between the water and the arch he could not tell, nor how deep the former. There was only one way in which he might learn these things, and that was to lower himself into the stream. For only an instant he hesitated weighing his chances. Behind him lay almost certainly the horrid fate of An-Tak; before him nothing worse than a comparatively painless death by drowning. Holding his haversack above his head with one hand he lowered his feet slowly over the edge of the narrow platform. Almost immediately he felt the swirling of cold water about his ankles, and then with a silent prayer he let himself drop gently into the stream. Great was Bradley's relief when he found the water no more than waist deep and beneath his feet a firm, gravel bottom. Feeling his way cautiously he moved downward with the current, which was not so strong as he had imagined from the noise of the running water. Beneath the first arch he made his way, following the winding curvatures of the right-hand wall. After a few yards of progress his hand came suddenly in contact with a slimy thing clinging to the wall--a thing that hissed and scuttled out of reach. What it was, the man could not know; but almost instantly there was a splash in the water just ahead of him and then another. On he went, passing beneath other arches at varying distances, and always in utter darkness. Unseen denizens of this great sewer, disturbed by the intruder, splashed into the water ahead of him and wriggled away. Time and again his hand touched them and never for an instant could he be sure that at the next step some gruesome thing might not attack him. He had strapped his haversack about his neck, well above the surface of the water, and in his left hand he carried his knife. Other precautions there were none to take. The monotony of the blind trail was increased by the fact that from the moment he had started from the foot of the ladder he had counted his every step. He had promised to return for An-Tak if it proved humanly possible to do so, and he knew that in the blackness of the tunnel he could locate the foot of the ladder in no other way.