No man in the whole of our great feverish London was so full of constant anxiety, frantic fear, and breathless bewilderment as myself. Ah, how I existed through those grey, gloomy March days I cannot explain. The mystery of it all was inscrutable. I should, I knew, be able to satisfy myself as to poor Mabel's fate if only I could clear up the mystery of who killed Professor Greer. This tension of nerves and constant longing for the return of the one for whom I held such a great and all-absorbing love was now telling upon my health. I ate little, and the mirror revealed how pale, careworn, and haggard I had become. Since the dawn of the New Year I was, alas! a changed man. In two months I had aged fully ten years. From inquiries I made of men interested in science and in chemistry I had discovered how great a man was the dead Professor, and how beneficial to mankind had been certain of his discoveries. Fate--or is it some world spirit of tragic-comedy?--plays strange pranks with human lives now and then, and surely nothing more singular ever happened in our London life of to-day than what I have already narrated in these pages. And to that thin, grey-faced neighbour of mine--the man who led a double life--was due the blame for it all. Though I made every endeavour and every inquiry, I could not learn what was his profession. That he was a man of means, a constant traveller, and well known in clubland, was all the information I could obtain. You will wonder, perhaps, why I did not go again to Whitehall Court and force the truth from the fellow's lips. Well, I hesitated, because in every argument I had had with him he had always won and always turned the tables upon myself. I had made a promise which, however justifiable my action, I had, nevertheless, broken. I had denounced him to the police, believing that I should see him arrested and charged. Yet, on the contrary, the authorities refused to lift a finger against him. What could I think? What, indeed, would you have thought in the circumstances? How would you have acted? One morning I had gone out early with Drake, trying the chassis of a new "twenty-four," and finding ourselves in front of the grey old cathedral at Chichester, we pulled up at the ancient "Dolphin" to have luncheon. My mind had been full of Mabel all the way, and though I had driven I had paid little or no attention to the car's defects. Dick Drake, motor enthusiast as he was, probably regarded my preoccupied manner as curious, but he made no comment, though he had no doubt noted all the defects himself. I had lunched in the big upstairs room--a noble apartment, as well known to travellers in the old coaching days as to the modern motorist--and had passed along into another room, where I lit a cigarette and stretched myself lazily before the fire.