"Listen carefully to the facts, Holford," urged Kirk. "The Professor's peril lies in the knowledge possessed by one man--yourself. It is therefore but just that you should know the truth." "I do not expect the truth from you," I laughed. "How can I, after all that has passed?" "The deceit I've practised upon you has been imperative," was his audacious answer. "Let me explain," interrupted the impostor, advancing to the fireplace near which I stood. "First, I repeat that I am Professor Ernest Greer, and that this is my house. My statement can be verified later, but for the present I ask you to accept it as the truth. My old friend here, Kershaw Kirk, is not an adventurer, though he so often poses as such. But it is under necessity, for his real profession is that of a confidential agent of the British Government, the trusted head official of our Intelligence Department." At this I smiled incredulously, wondering what fantastic story he was about to relate, for even then I did not recognise him by the photograph I had obtained just before going up to Scotland. He was thinner, and his eyes were quite unlike those of the photograph, being narrower and deeper set. "The plain facts are as follows," he went on, after a second's pause. "I had been experimenting until I had discovered an easy method of obtaining from the air those subtle elements helium and neon. My success had incidentally confirmed Sir William Ramsay's estimation that the proportion of neon and helium in the atmosphere was about one to two in each hundred thousand, when a suggestion occurred to me that my process of hardening armour plates might be improved upon, and a substance of great cutting power created. My experiments were long and tedious, but were at last crowned with success. I very foolishly gave, in the French scientific journal _Cosmos_, some account of these experiments, and a month later I was secretly informed by Kirk that the German Government--always our rivals where improvements in war material are concerned--was actively endeavouring to obtain my secret. As you know, I always kept my laboratory locked, and allowed no one within upon any pretext. My only confidante was my daughter Ethelwynn." And again he paused, glancing across at where Kirk stood, narrow-eyed and silent.