His search was unavailing; the mysterious reptile was not to be found. Returning again to the study he seated himself behind the table, facing the door--which he left ajar. Ten minutes passed in silence--only broken by the dim murmur of the distant traffic. He had almost persuaded himself that his imagination--quickened by the atmosphere of mystery and horror wherein he had recently moved--was responsible for the hiss, when a new sound came to confute his reasoning. The people occupying the chambers below were moving about so that their footsteps were faintly audible; but, above these dim footsteps, a rustling--vague, indefinite, demonstrated itself. As in the case of the hiss, it proceeded from the passage. A light burnt inside the outer door, and this, as Cairn knew, must cast a shadow before any thing--or person--approaching the room. _Sssf! ssf!_--came, like the rustle of light draperies. The nervous suspense was almost unbearable. He waited. _What_ was creeping, slowly, cautiously, towards the open door? Cairn toyed with the trigger of his revolver. "The arts of the West shall try conclusions with those of the East," he said. A shadow!... Inch upon inch it grew--creeping across the door, until it covered all the threshold visible. Someone was about to appear. He raised the revolver. The shadow moved along. Cairn saw the tail of it creep past the door, until no shadow was there! The shadow had come--and gone ... but there was _no substance_! "I am going mad!" The words forced themselves to his lips. He rested his chin upon his hands and clenched his teeth grimly. Did the horrors of insanity stare him in the face! From that recent illness in London--when his nervous system had collapsed, utterly--despite his stay in Egypt he had never fully recovered. "A month will see you fit again," his father had said; but?--perhaps he had been wrong--perchance the affection had been deeper than he had suspected; and now this endless carnival of supernatural happenings had strained the weakened cells, so that he was become as a man in a delirium! Where did reality end and phantasy begin? Was it all merely subjective? He had read of such aberrations. And now he sat wondering if he were the victim of a like affliction--and while he wondered he stared at the rope of silk. That was real. Logic came to his rescue. If he had seen and heard strange things, so, too, had Sime in Egypt--so had his father, both in Egypt and in London! Inexplicable things were happening around him; and all could not be mad! "I'm getting morbid again," he told himself; "the tricks of our damnable Ferrara are getting on my nerves. Just what he desires and intends!" This latter reflection spurred him to new activity; and, pocketing the revolver, he switched off the light in the study and looked out of the window.