All the lights had been lowered, save for a single bracket lamp, which shone on Regnier’s melancholy but expressive face. As he began, the storm changed its key, and came in steady, driving force rather than in great gusts. “It really began that night at Mrs. Hartnell’s,” he said reflectively. “I was tremendously impressed by that second letter which came out from beneath the visible one and, try as I would, I could not shake off a feeling that the message was true; that the man who wrote possessed some strange and awful power, which would make it possible for him to do what he threatened. When I left you that night, I could not sleep. I looked at the problem from every side, and finally analyzed it down to this. If ‘the man’ is to do this, he must either be a great scientist himself, or have obtained his secret from some great scientist. I went further. I made up my mind that the most probable line of work to produce such a destroying agent would be along the lines of radio-active experiments. In consequence, I went directly to work, and with the help of two assistants, I reviewed all the literature of radio-active matter which had appeared in the last five years, and made a digest of the papers, their subjects and their authors. Then came my time of sailing for abroad, and I took the digest with me. I spent most of my time on the way over in a systematic sorting out of the men who had made the greatest advances, and who would be the most likely to obtain some great result. I finally narrowed my choice down to five. One of the five was Heidenmuller. He had published his last paper in the _Zeitschrift fur Physicalische Chemie_ in April, 19--, and had published nothing since. As soon as I landed I hastened to get a file of the magazine, and found that in a somewhat deeply technical paper he had spoken of the possibility that a radio-active agent, powerful enough to give an ultimate resolution of any metal, might be obtained. That was enough for me; I started straight for London and Heidenmuller. As you know, I found him dead, but I heard the story of his death and I knew by that time that if he had possessed the secret, he must have passed it on to some one else. So I went to work. I did not look up Swenton because I found that Heidenmuller’s first assistant, Griegen, had gone as wireless operator on one of the big yachts then at Cowes. So I went down there, chartered a small yacht, and spent a week hunting for Griegen. I think I wrote you from there,” he said to Dorothy. “You did,” she replied.