Murdock's interlocutor, whoever he had been, had disappeared. But how? The question interested Sturgis, and his mind at once began to seek an answer to it. There were three doors leading from the study. One of these was the one by which Murdock and Sturgis had just entered from the hall. No one could have passed out that way without meeting them. Then there were the folding-doors leading into the library; but, as the door leading from the library to the hall had remained slightly ajar, Sturgis felt sure that he would have heard the man had he gone out by that way. The third door led to a small extension. "He must have gone into the extension," thought Sturgis. The only alternative was an exit through the windows. This in itself would not have presented any special difficulty; for the distance to the flagging below was hardly more than twelve or thirteen feet. But the yard, which was of diminutive size on account of the space allotted to the garden on the street, was inclosed by an unusually high fence protected by a row of sharp and closely set spikes. These looked so formidable that the thought of any one attempting to scale the fence instantly suggested visions of impaled wretches writhing in Oriental tortures. The only possible exit from the yard, therefore, seemed to be through the basement; that is to say, past the kitchen and the servants' department. All these thoughts flashed through the reporter's brain in a small fraction of the time which is required to record them. They occurred to him unbidden, while his conscious efforts were centered upon discovering how Chatham had managed to escape from the rear of the Manhattan Chemical Company's building. This Sturgis recognized without much difficulty. It was directly in line with the house in which he now was, and its yard did not differ from the neighboring ones, the fences of which could be scaled without much trouble. Chatham evidently might have passed into any one of several buildings which lacked the protection of the formidable spikes that so effectually guarded the approach to Murdock's house from the rear. One point, however, was puzzling. Why should Chatham take the trouble and the risk of scaling fences in broad daylight, only to return a few hours later by the street door under the very noses of the detectives from whom he had presumably wished to escape? There seemed to be no plausible answer to this question. But Sturgis was not given much time in which to consider it; for Murdock, who had waited for him to broach the subject of his interview, now coldly remarked: "Perhaps, Mr. Sturgis, you will be good enough to inform me to what I owe the honor of this visit?" Sturgis took as a pretext the first subject which came into his mind.